Bookmark AI

Fix broken env overrides, stale vector store, and encoding issues

- Fix config import pattern: use `from . import config` so env var
  overrides (LLM_MODEL, EMBEDDING_MODEL, etc.) take effect at runtime
  instead of being captured at import time
- Fix requirements.txt: rewrite as UTF-8 with direct deps only
  (was UTF-16 with ~99 transitive deps)
- Add stale document removal from FAISS via indexed_urls.json sidecar,
  replacing private docstore._dict API usage
- Add incremental cache saving during description generation via
  on_progress callback (saves every 10 completions)
- Include folder path in document content and metadata for better
  folder-based search
- Remove legacy pickle migration code and pickle import

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>