Add label review web app and apply-edits CLI
- src/review_app.py: FastAPI app serving a browser UI for paging through
dataset items, marking reviewed/flagged, and editing labels inline.
State persists in data/review.db (SQLite, git-ignored). Items table
reloads from manifests each startup; reviews/flags/edits are durable.
Cursor-based pagination, server-side filtering (pending/reviewed/
flagged/edited/all), per-split stats in toolbar.
- src/static/review.html: vanilla JS frontend. All interactions go
through an `actions` object; keyboard shortcut hook is stubbed out
(commented) for easy wiring later.
- src/apply_edits.py: CLI to flush edits table -> manifest.jsonl files,
with --dry-run and per-split filtering. Prints dvc add / git commit
instructions on completion.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>