fix(hosts): reject or infer a missing authType on host create

[ZacharyZcR]

Summary

Creating an SSH host via POST /host/db/host without authType returned HTTP 500 "Failed to save SSH data": the route passed authType: undefined straight to the insert, which violates NOT NULL ssh_data.auth_type. Real case: the Termix CLI hosts create --credential-id 2 ... without --auth-type.

Changes (create route):

• When the body names no authType/authMethod, infer it the way the UI sends hosts: credentialId ⇒ credential, key ⇒ key, password ⇒ password.
• Host defaults still apply as before: a body that leaves auth out inherits core.auth from the user/folder/server defaults, so such a create keeps succeeding.
• If nothing (body, inference, defaults) supplies an auth type, answer 400 authType is required (password, key, credential, agent or none) instead of letting the DB constraint throw.

Create and update: a non-string authType/authMethod (e.g. an object) is now a 400 instead of a 500 from the driver. Unknown string values are still accepted on purpose, since plugin auth types may be saved while their plugin is disabled and fail at connect with a message naming the plugin.

Update was checked separately: leaving authType out keeps the stored value (the column is not written), so it never hit the constraint.

Test plan

• New host-create-auth-type.test.ts drives the real host router against in-memory SQLite: credentialId-only and password-only creates succeed with the inferred type; an auth-less create returns 400; an auth-less create inherits core.auth from user defaults; an update without authType keeps the stored type; an update with a non-string authType returns 400. The create/update failure cases returned 500 before the fix.
• Unit test for impliedSshAuthType
• npx vitest run src/backend/tests/database/routes src/backend/tests/hosts/defaults (391 passed)
• eslint, prettier 3.9.6, tsc -p tsconfig.app.json

[termix-triage-bot]

AI review | Looks safe to merge

Adds validation and fallback inference for authType on host creation and update to prevent database constraint violations. Includes comprehensive tests, follows path mirroring and mocking rules, and targets the correct dev branch.

_{Reviewed fccbb07. AI can be wrong, a maintainer still decides. Comment /termix review to run it again.}