tvOS playback with resume prompt and conversion gate

[altaywtf]

Parent

#123

What this delivers

tvOS playback at parity with the shipped TV app: system player, HLS-only, resume prompt, throttled position reporting, subtitle preferences, and the conversion gate.

Scope

• System AVPlayer surface (native transport controls, info panels) playing the SDK HLS stream URL; subtitles and audio tracks come from the HLS manifest.
• Resume prompt before playback when a position exists: "Continue from H:MM:SS" / "Start from the beginning" over the poster, honoring the remember-position setting.
• Start-from reporting throttled to the shipped cadence (15s, flush on exit); mark-watched state reflects back into the browser rows.
• Subtitle behavior: auto-select first track unless the don't-auto-select setting is on; hide entirely when subtitles are off.
• Conversion gate for needs-conversion files with live status, matching the browser child's row affordances.
• Playback errors are localized, recoverable, and reported to the error tracker.

Acceptance criteria

• Resume prompt appears exactly when a server position exists and the setting allows
• Positions reported during playback appear on other clients within the cadence
• Subtitle auto-select preferences behave per settings matrix
• Conversion gate converts and plays end-to-end

Verification

tvOS simulator recordings of resume, subtitle, and conversion flows; unit tests over the resume/reporting state machine.

Blocked by

• tvOS home and list-first file browsing #141

Boundaries

No custom transport UI (the shipped tvOS app uses system controls; so do we). No MP4 playback-type setting on tvOS (HLS-only, matching shipped behavior).