feat: implement Phase 2 core features
- Add document CRUD API (list/get/upload/update/delete with auth)
- Upload saves to Inbox + auto-enqueues processing pipeline
- Delete defaults to DB-only, explicit flag for file deletion
- Add hybrid search API (FTS 0.4 + trigram 0.2 + vector 0.4 weighted)
- Modes: fts, trgm, vector, hybrid (default)
- Vector search gracefully degrades if GPU unavailable
- Add Inbox file watcher (5min interval, new file + hash change detection)
- Register documents/search routers and file_watcher scheduler in main.py
- Add IVFFLAT vector index migration (lists=50, with tuning guide)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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