Persist symbol-kind filter readiness evidence

[Widthdom]

Summary

• persist normalized symbol-kind filter policy and per-file dropped-symbol audit evidence across CLI and MCP indexing
• derive CLI, status, workspace, and MCP readiness from the same persisted evidence, with conservative legacy and mixed-writer fallback
• warn on non-authoritative negative symbol/graph results across structured, formatted, JSON array, and NDJSON output without degrading unrelated file, text-search, or validation counts
• reject scoped updates when filter provenance is unavailable, and clear provenance immediately for interrupted destructive rebuilds

Validation

• dotnet build CodeIndex.sln --configuration Debug --no-restore — 0 warnings, 0 errors
• dotnet build CodeIndex.sln --configuration Release --no-restore — 0 warnings, 0 errors
• full Release net8 suite — 12,117 passed, 9 skipped, 0 failed
• full Release net9 suite — 11,632 passed, 431 skipped, 0 failed
• final FullyQualifiedName~Issue5224 Release runs — 13/13 passed on each TFM
• pipeline regression set (export/import, symlink watch, and Issue Persist symbol-kind filter omissions and report filtered indexes as incomplete #5224) — 17/17 passed on net8
• post-main-merge Issue5224|Issue5226 Release integration — 21/21 passed on each TFM
• validate count-envelope regression group — 14/14 passed
• changelog fragment validator — 3 fragments valid after latest main merge
• dogfood index/status/workspace — 1,465 files, 56,802 symbols, 530,627 references; fresh and complete; 2/2 workspace members healthy

Adversarial review

• completed the required two codex review --base origin/main rounds
• fixed all five actionable findings from round 1 and all three actionable findings from round 2, with regression coverage
• workflow review limit reached; final fixes were verified by builds, focused tests, integration tests, and dogfood checks

Documentation

• updated the bilingual README, USER_GUIDE, DEVELOPER_GUIDE, and COMPATIBILITY contracts
• updated AGENT_GUIDE.md status/readiness contract
• added changelog.d/unreleased/5224.fixed.md; CHANGELOG.md remains untouched

Follow-ups

• None.

Fixes #5224