Make inspect selectors reusable and overload-aware (#5159)

[Widthdom]

Summary

• Add reusable inspect symbol selectors with generation provenance, stale and cross-database rejection, pagination continuity, CLI help, completions, and MCP parity.
• Return candidate-scoped overload evidence and truthful identity_scope_reason metadata instead of duplicating merged references and callers.
• Narrow C# overload candidates only for conservative positional arity matches, including rank-5 fallback resolution, while preserving ambiguity for optional, partial, raw-string, generic, named, params, extension, malformed, and other binding-sensitive cases.
• Document the selector and overload contracts in both English and Japanese and add changelog fragment 5159.fixed.md.

Validation

• dotnet build CodeIndex.sln --no-restore --configuration Debug: passed with 0 warnings and 0 errors.
• Full regression suite before the latest passing main sync: net8.0 11,839 passed, 9 skipped, 0 failed; net9.0 11,359 passed, 426 skipped, 0 failed.
• Final post-sync integration tests for Issues 5158 and 5159 plus the reference-contract migration: 22 passed on net8.0 and 22 passed on net9.0.
• Issue 5159 focused suite: 19 passed on both net8.0 and net9.0.
• dotnet format verify, changelog validation, and git diff check: passed.
• Final local index status: fold, graph, reference graph, SQL graph contract, hotspot family, and index readiness are all current.

Adversarial review

• Completed the required two Codex adversarial review rounds.
• Addressed all findings covering optional attributes, incomplete calls, selector path and language filters, raw strings, partial methods, and rank-5 C# fallback resolution.

Fixes #5159

Collaborator checklist

• The change follows the existing code style.
• The change includes tests when behavior changes.
• The change includes a changelog fragment when user-visible behavior changes.
• Documentation has been updated when needed.