Default development server to loopback and preserve bind interface

[rochacbruno]

The development server previously defaulted to all interfaces, and a failed explicit loopback bind could fall back to all interfaces. Default --serve to 127.0.0.1:8000 and preserve the requested IPv4/IPv6 interfaces when retrying on an OS-assigned port. Explicit network binds remain supported.

Label the server as development-only in CLI help, source comments, terminal startup output, and documentation. Add binding regression tests and a draft release note.

This intentionally addresses only binding defaults/fallback and development-only messaging. Editor/API behavior is unchanged; no authentication, CSRF/CORS checks, or filesystem restrictions are introduced. This does not resolve the broader path-traversal findings.

Related to #554.

Validation: formatting, Clippy with warnings denied, the full unit/integration test suite, and mask pedantic passed with Rust 1.96. The example site also builds successfully.

Browser visual verification could not run because the browser tool rejected this session's API-key authentication. The preview server started successfully on loopback and printed the development-only message.

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imd_flag-5fa03e3c45b4101d.rmeta --extern raw_cpuid=/__w/marmite/marmite/target/debug/build/raw-cpuid/30a1f1dd5e7c8b41/out/libraw_cpuid-30a1f1dd5e7c8b41.rmeta --extern reborrow=/__w/marmite/marmite/target/debug/build/reborrow/608cbab27e87df87/out/libreborrow-608cbab27e87df87.rmeta --cap-lints allow -Cdebuginfo=2 -Cstrip=none --cfg=tarpaulin -Clink-dead-code --force-warn=unused_crate_dependencies --cfg libpulp_const --check-cfg 'cfg(libpulp_const)'`
   Compiling loop9 v0.1.5
     Running `/usr/local/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name loop9 --edition=2021 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/loop9-0.1.5/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat,unused-externs-silent --crate-type lib --emit=dep-info,metadata,link -Z embed-metadata=no -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=9c129ef033b6f569 -C extra-filename=-9ec02478d2a9945c --out-dir /__w/marmite/marmite/target/debug/build/loop9/9ec02478d2a9945c/out --extern imgref=/__w/marmite/marmite/target/debug/build/imgref/57a6aa3332a968b6/out/libimgref-57a6aa3332a968b6.rmeta --cap-lints allow -Cdebuginfo=2 -Cstrip=none --cfg=tarpaulin -Clink-dead-code --force-warn=unused_crate_dependencies`
   Compiling signal-hook-registry v1.4.8
     Running `/usr/local/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name signal_hook_registry --edition=2015 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/signal-hook-registry-1.4.8/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat,unused-externs-silent --crate-type lib --emit=dep-info,metadata,link -Z embed-metadata=no -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values())' -C metadata=8024cd3c8d41f0a9 -C extra-filename=-02b07fb660933ed3 --out-dir /__w/marmite/marmite/target/debug/build/signal-hook-registry/02b07fb660933ed3/out -L dependency=/__w/marmite/marmite/target/debug/build/libc/c780a52bb6a83b7d/out --extern errno=/__w/marmite/marmite/target/debug/build/errno/899025afc602f07e/out/liberrno-899025afc602f07e.rmeta --extern libc=/__w/marmite/marmite/target/debug/build/libc/c780a52bb6a83b7d/out/liblibc-c780a52bb6a83b7d.rmeta --cap-lints allow -Cdebuginfo=2 -Cstrip=none --cfg=tarpaulin -Clink-dead-code --force-warn=unused_crate_dependencies`
   Compiling notify v6.1.1
     Running `/usr/local/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name notify --edition=2021 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/notify-6.1.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat,unused-externs-silent --crate-type lib --emit=dep-info,metadata,link -Z embed-metadata=no -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="crossbeam-channel"' --cfg 'feature="default"' --cfg 'feature="fsevent-sys"' --cfg 'feature="macos_fsevent"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("crossbeam-channel", "default", "fsevent-sys", "kqueue", "macos_fsevent", "macos_kqueue", "manual_tests", "mio", "serde", "timing_tests"))' -C metadata=44ccc7aadab90164 -C extra-filename=-c2ad7b092d724c28 --out-dir /__w/marmite/marmite/target/debug/build/notify/c2ad7b092d724c28/out -L dependency=/__w/marmite/marmite/target/debug/build/bitflags/92e079e44f352a5f/out -L dependency=/__w/marmite/marmite/target/debug/build/cfg-if/cfa8c34b3dabb49b/out -L dependency=/__w/marmite/marmite/target/debug/build/crossbeam-utils/b94190a01fe60930/out -L dependency=/__w/marmite/marmite/target/debug/build/inotify-sys/649e5282f1255025/out -L dependency=/__w/marmite/marmite/target/debug/build/libc/c780a52bb6a83b7d/out -L dependency=/__w/marmite/marmite/target/debug/build/log/bd28dd8cd3a50d9e/out -L dependency=/__w/marmite/marmite/target/debug/build/same-file/f4b85417f1720abf/out --extern crossbeam_channel=/__w/marmite/marmite/target/debug/build/crossbeam-channel/c560dcec9872e329/out/libcrossbeam_channel-c560dcec9872e329.rmeta --extern filetime=/__w/marmite/marmite/target/debug/build/filetime/78cf49152239f13e/out/libfiletime-78cf49152239f13e.rmeta --extern inotify=/__w/marmite/marmite/target/debug/build/inotify/eb7b2bdf8c033e2b/out/libinotify-eb7b2bdf8c033e2b.rmeta --extern libc=/__w/marmite/marmite/target/debug/build/libc/c780a52bb6a83b7d/out/liblibc-c780a52bb6a83b7d.rmeta --extern log=/__w/marmite/marmite/target/debug/build/log/bd28dd8cd3a50d9e/out/liblog-bd28dd8cd3a50d9e.rmeta --extern mio=/__w/marmite/marmite/target/debug/build/mio/46ed096e41cd9996/out/libmio-46ed096e41cd9996.rmeta --extern walkdir=/__w/marmite/marmite/target/debug/build/walkdir/64885f6ceffc20ac/out/libwalkdir-64885f6ceffc20ac.rmeta --cap-lints allow -Cdebuginfo=2 -Cstrip=none --cfg=tarpaulin -Clink-dead-code --force-warn=unused_crate_dependencies`
     Running `/__w/marmite/marmite/target/debug/build/arborium-fsharp/bb94a44023fd1152/out/build_script_build`
     Running `/__w/marmite/marmite/target/debug/build/arborium-json/4d97a106a682e848/out/build_script_build`
     Running `/__w/marmite/marmite/target/debug/build/arborium-svelte/dd2aff064b8e11ee/out/build_script_build`
�[2m2026-09-29T14:38:30.224133Z�[0m �[34mDEBUG�[0m �[2mcargo_tarpaulin::cargo�[0m�[2m:�[0m Linker paths: ["/usr/local/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib", "/__w/marmite/marmite/target/debug/build/arborium-jsdoc/fc36a99f2856e6aa/out", "/__w/marmite/marmite/target/debug/build/arborium-javascript/de6de70c17fbe3bd/out", "/__w/marmite/marmite/target/debug/build/arborium-css/e0c4380310d1bdc9/out", "/__w/marmite/marmite/target/debug/build/arborium-c/09c8aa07b2855949/out", "/__w/marmite/marmite/target/debug/build/arborium-html/edfa113c6b4e9db8/out", "/__w/marmite/marmite/target/debug/build/ring/3818a4fc692f86d2/out", "/__w/marmite/marmite/target/debug/build/arborium-scss/fdde8207d234daa1/out", "/__w/marmite/marmite/target/debug/build/arborium-tree-sitter/f37deb2b739fb2da/out", "/__w/marmite/marmite/target/debug/build/arborium-typescript/f6f3191cf1443d09/out", "/__w/marmite/marmite/target/debug/build/zstd-sys/c2ffd8b4b91393f6/out", "/__w/marmite/marmite/target/debug/build/arborium-toml/9334cee6b4ed39ba/out", "/__w/marmite/marmite/target/debug/build/arborium-yaml/580a7c9e6e2993d8/out", "/__w/marmite/marmite/target/debug/build/arborium-cpp/e06928ca9450d272/out", "/__w/marmite/marmite/target/debug/build/arborium-json/9aeadf1b044f14f5/out"]
error: Broken pipe (os error 32)
warning: build failed, waiting for other jobs to finish...
error: could not compile `pulp` (lib) due to 10 previous errors

Caused by:
  process didn't exit successfully: `/usr/local/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name pulp --edition=2021 /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pulp-0.22.3/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat,unused-externs-silent --crate-type lib --emit=dep-info,metadata,link -Z embed-metadata=no -C embed-bitcode=no -C debuginfo=2 --cfg 'feature="default"' --cfg 'feature="relaxed-simd"' --cfg 'feature="std"' --cfg 'feature="x86-v3"' --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("default", "macro", "nightly", "relaxed-simd", "std", "x86-v3", "x86-v4"))' -C metadata=49c6d26396880696 -C extra-filename=-267e5b9160e0d506 --out-dir /__w/marmite/marmite/target/debug/build/pulp/267e5b9160e0d506/out -L dependency=/__w/marmite/marmite/target/debug/build/bitflags/358e566ab75a077d/out -L dependency=/__w/marmite/marmite/target/debug/build/bytemuck/5cd59610090a74df/out -L dependency=/__w/marmite/marmite/target/debug/build/num-traits/e961cf18440cd68d/out --extern bytemuck=/__w/marmite/marmite/target/debug/build/bytemuck/5cd59610090a74df/out/libbytemuck-5cd59610090a74df.rmeta --extern cfg_if=/__w/marmite/marmite/target/debug/build/cfg-if/cfa8c34b3dabb49b/out/libcfg_if-cfa8c34b3dabb49b.rmeta --extern libm=/__w/marmite/marmite/target/debug/build/libm/fc62884bc3286f32/out/liblibm-fc62884bc3286f32.rmeta --extern num_complex=/__w/marmite/marmite/target/debug/build/num-complex/12c105d6bfc3b668/out/libnum_complex-12c105d6bfc3b668.rmeta --extern paste=/__w/marmite/marmite/target/debug/build/paste/6b7b026d5d765873/out/libpaste-6b7b026d5d765873.so --extern pulp_wasm_simd_flag=/__w/marmite/marmite/target/debug/build/pulp-wasm-simd-flag/5fa03e3c45b4101d/out/libpulp_wasm_simd_flag-5fa03e3c45b4101d.rmeta --extern raw_cpuid=/__w/marmite/marmite/target/debug/build/raw-cpuid/30a1f1dd5e7c8b41/out/libraw_cpuid-30a1f1dd5e7c8b41.rmeta --extern reborrow=/__w/marmite/marmite/target/debug/build/reborrow/608cbab27e87df87/out/libreborrow-608cbab27e87df87.rmeta --cap-lints allow -Cdebuginfo=2 -Cstrip=none --cfg=tarpaulin -Clink-dead-code --force-warn=unused_crate_dependencies --cfg libpulp_const --check-cfg 'cfg(libpulp_const)'` (exit status: 1)
�[2m2026-09-29T14:38:33.168090Z�[0m �[31mERROR�[0m �[2mcargo_tarpaulin�[0m�[2m:�[0m Failed to compile tests!
error[E0080]: evaluation panicked: assertion failed: core::mem::size_of::<T>() == core::mem::size_of::<U>()
    --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pulp-0.22.3/src/lib.rs:3291:3
     |
3291 |         assert!(core::mem::size_of::<T>() == core::mem::size_of::<U>());
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `CheckSameSize::<i8, u16>::VALID` failed here


Error: "Failed to compile tests!\nerror[E0080]: evaluation panicked: assertion failed: core::mem::size_of::<T>() == core::mem::size_of::<U>()\n    --> /usr/local/cargo/registry/src/index.crates.io-1949cf8c6b5b557f/pulp-0.22.3/src/lib.rs:3291:3\n     |\n3291 |         assert!(core::mem::size_of::<T>() == core::mem::size_of::<U>());\n     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ evaluation of `CheckSameSize::<i8, u16>::VALID` failed here\n\n"

[github-actions]

Pedantic Clippy

No pedantic warnings found.