[feature-media] Theme audio preview does not start (controls stay at 0:00)

[wax911]

Description of Bug

Audio preview playback in the media theme bottom sheet does not start at runtime even though the playback UI is enabled and responsive.

The sheet now shows playback controls (play/pause + seek), but pressing play keeps the row in a non-playing state with Not available and 0:00 / 0:00 on current runtime data.

Reproduction Steps

1. Install latest co.anitrend debug build.
2. Open a media detail page with theme variants (example used during validation: Kimetsu no Yaiba).
3. Open Anime themes section.
4. Tap a theme row to open the bottom sheet.
5. Tap Audio on a variant/hero preview that should be playable.

Actual Result

• Playback does not start.
• Duration remains 0:00 / 0:00.
• Sheet may show Not available for audio stream in current runtime path.

Expected Result

• If a valid audio URL exists, playback should start and position/duration should update.
• If source is invalid/unavailable, user should receive explicit failure reason and retry guidance.

Device & Build Information

• OS Version: Android 15 (API 35 emulator)
• App Variant: co.anitrend (installGoogleDebug)
• Hardware/Model: sdk_gphone64_x86_64 emulator
• Download Source: Github

Additional Context

This is being tracked as Phase 2 of media theme playback rollout.

Related implementation commits:

• 18e173a7d feat(media): enrich theme variants and section metadata
• fd54569a4 test(media): validate theme playback states

The new playback UX/spec work is complete, but runtime audio stream activation still fails and needs focused debugging + hardening.