Provider filter (#4):
- client.discover() + engine.discover_filter() take a TMDB provider id and pass
with_watch_providers + watch_region (engine._region) + flatrate. Browse gets a
streaming-service chip row (Netflix/Prime/Disney+/Max/Apple TV+/Hulu/Paramount+/
Peacock); the grid title reflects 'on <service>'.
Infinite scroll (#6):
- Grid paginates via an IntersectionObserver sentinel (600px lookahead) with a
bottom spinner; the Load more button stays only as a no-IO fallback.
Polish (#7):
- Hero keyboard nav (←/→ when Discover is the visible view, ignoring inputs and
while the trailer is open); focus-visible rings on chips/segments/cards/arrows.
Note: 'complete-the-franchise' rail (#5) needs a collection_id per movie, which
the schema doesn't store yet — deferred (would need an enrichment pass).
Tests: +1 (provider watch_region params); updated the discover_filter fake for
the new kwargs. Enrichment + API suites: 115 passed.
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