docs: add FTS architecture docs + fix fulltext docstring

feat: core pipeline + FastAPI API (Phases 0-6) ...

Implemented the full VMK Data Collector foundation and processing pipeline:

- Config, logging, exception hierarchy
- DB models (listings, raw data, images, snapshots, enrichments, custom fields)
- Alembic async migrations
- Repositories with upsert/snapshot support
- Domain entities and Pydantic schemas
- Ollama AI client with mock mode
- AI normalizer, image analyzer, enricher
- Image downloader with SHA-256 dedup
- PropertyPipeline: raw -> AI validate -> upsert/snapshot -> images -> enrich
- FastAPI app with /api/v1/ingest endpoint

Co-Authored-By: Claude <noreply@anthropic.com>