feat: add match breakdown tooltip and TMDB poster support

[cheangie]

Summary

Adds two new frontend features and wires up TMDB poster image support in the backend data loader.

• Adds a hoverable match breakdown tooltip to the % similarity badge on each title card — shows per-field TF-IDF scores (Description, Genres, Cast, Director) plus IMDb and Popularity signals as a mini bar chart overlaying the card face
• Adds the same hoverable breakdown to the % match text in the detail drawer via a DrawerMatchBadge component
• Adds poster image support to TitleCard — renders item.poster_url as a full-bleed cover image when available, falls back to monogram initials until the backend provides it
• Adds TMDB poster fetching to data_loader.py with a disk cache (data/poster_cache.csv) so TMDB is only queried once on first startup — subsequent restarts load instantly from cache

Frontend changes

File	Description
frontend/src/App.jsx	Added MatchTooltip, DrawerMatchBadge components; hoverable badge on TitleCard; poster image support with monogram fallback

Backend changes

File	Description
backend/data_loader.py	Added _fetch_poster_url, _build_poster_cache; TMDB API config via TMDB_API_KEY env var; poster_url column added to master DataFrame

What needs to happen on the backend before posters work

1. Set TMDB_API_KEY as an environment variable on the server
2. Add poster_url: Optional[str] = None to TitleResult in main.py
3. Return poster_url in the /recommend and /title responses

The frontend is already wired — the moment poster_url exists in the API response, posters appear automatically with no further frontend changes needed.

[LavishSphere]

requirements.txt not updated

[LavishSphere]

Lint is also failing, everything else looks fine.

[LavishSphere]

LGTM