add vector similarity search and tombstone tracking
- add /similar endpoint for finding semantically related documents
- add tombstones table for tracking deleted records
- backfill script for embedding documents via Voyage AI (3470 docs done)
- show "related to [top result]" section at bottom of search results
- helper scripts for checking vector index and testing queries
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>