v0.52.0 - Fresher indexes and leaner MCP payloads

What's changed

• Added shared, read-only repository index health checks.
• MCP orientation tools now detect changed, deleted, unindexed files and extractor drift.
• Reading plans, traces, callers and related-file results exclude deleted paths.
• Added compact MCP responses for related-file and symbol-callers tools.
• Full contracts remain available through include_details=true.
• Session close now reports repository index freshness and avoids duplicate memory suggestions.
• Doctor now reuses the shared index-health logic.
• Updated the Codex skill and MCP documentation.
• Added focused tests for stale indexes, deleted files, memory deduplication and compact payloads.

Verification

• Full test suite passed.
• git diff --check passed.
• Bundled and source skill copies are synchronized.