The video Library Scan tool only scanned 'all' — but movies and TV are
independent libraries (unlike music's single library). The scanner backend
already supported media_type='movie'|'show'|'all'; this just wires it up:
- /api/video/scan/request now reads media_type and threads it to request_scan
- the Tools card gains a target selector (All / Movies Only / TV Shows Only)
alongside the existing mode dropdown, matching the music scan's UX
- the live status detail reflects the target (no confusing '0 shows' on a
movies-only scan)
Seam test: the endpoint passes both mode and media_type through (default all/full,
explicit movie/deep, TV-only). Existing scanner media-type/scope tests unchanged.
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