Remove ClickHouse data store support

[zhangzhenghao]

Summary

• Remove the ClickHouse data backend, URI registration and configuration support.
• Delete ClickHouse-specific SQL paths, helper tables/materialized views, search implementation, tests and benchmarks.
• Remove ClickHouse driver dependencies, CI service, Compose examples and documentation references.
• Keep the shared Optimize interface as a no-op and preserve the remaining data backends.

Breaking change

ClickHouse data stores (clickhouse://, chhttp:// and chhttps://) are no longer supported. Existing users must migrate their data/configuration before upgrading. No existing database is modified by this PR.

Validation

• Local tests/builds skipped at user request. Preliminary attempts before that request were blocked by module-cache I/O and Go 1.26.1 being older than required Go 1.27.0; no tests completed.
• Go files formatted. Dependencies removed explicitly; go mod tidy not run.
• Initial CI passed integration tests and lint; unit tests failed due to incorrect assertions in the newly added TestDataStore. Both newly added rejection tests have now been removed at user request; CI rerun pending.

Independent PR against master; does not modify #1392.

[codecov]

Codecov Report

❌ Patch coverage is 96.84211% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.20%. Comparing base (646cfef) to head (6264f3e).

Files with missing lines	Patch %	Lines
storage/data/sql.go	96.84%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1393      +/-   ##
==========================================
- Coverage   79.30%   79.20%   -0.10%     
==========================================
  Files          92       92              
  Lines       16693    16406     -287     
==========================================
- Hits        13239    12995     -244     
+ Misses       3454     3411      -43     

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