feat: add server-side HLS transcoding

[mahoshojoHCG]

Summary

• add server-side media probing with direct-play, remux, and selective transcode planning
• stream progressive tokenized HLS through a bounded worker queue with cancellation, hardware fallback, resource limits, persistent versioned cache, and TTL/LRU cleanup
• move incompatible MKV fallback from browser FFmpeg WASM to HLS.js while preserving direct playback, progress restore, subtitle preferences, external players, and next-episode autoplay
• expose session state and transcoding metrics, package FFmpeg, and document operational settings
• cover planning, cache reuse/invalidation, queueing, cancellation/failure cleanup, real FFmpeg HLS/WebVTT output, controller behavior, and authenticated/anonymous API boundaries

Verification

• dotnet test SecondDimensionWatcherReDive.slnx -c Release --no-restore
• yarn install --immutable
• yarn test
• yarn build
• yarn node --check mock-server.mjs
• podman build -f Containerfile -t localhost/sdw-issue-11-test .
• verified ffmpeg and ffprobe execute inside the built image

Closes #11

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-08-29T15:24:46.061710Z	30192c9	PR opened

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Reviewed commit: 30192c9d34

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