feat(core): expose video tracks & renditions on the SPF media adapter

[spuppo-mux]

Part 1 of #1795 (video → audio → streamType → live → parity/autoplay).

What: SimpleHlsMedia now projects the SPF engine's video renditions onto the standard videoTracks / videoRenditions DOM surface (read, write, events) so a quality menu binds to it with no adapter-specific code, matching HlsJsMedia.

How:

• The HLS SPF engine gains a derived videoRenditions signal (new deriveVideoRenditions behavior, mirroring deriveCdnPriority): projects the resolved presentation's video switching set, clears on src unload, skips writes when a reload carries the same set.
• A core projection mixin (SimpleHlsMediaMediaTracksMixin) subscribes to that signal via effect, builds one selected main video track + a VideoRendition per level, and writes selection back:
  • selectedIndex → userVideoTrackSelection = { selectedIndex },
  • -1 → clear (ABR).

Design decisions:

• Tried to follow the no SPF -> core dependency rule. Initially had everything implemented in core, then moved part to SPF with the behavior.
• SPF publishes model vocabulary (bandwidth, codecs[], FrameRate); core owns DOM mapping (codecs.join(','), FrameRate → number). Kept them in the mixin file since they are only used there, but could move as helpers later.
• Re-wire on src: the adapter currently destroys+recreates the engine per src, so subscriptions re-wire via one AbortController per connect.
• Order = manifest declaration order (what SPF already handled), deterministic but unsorted. Not sorted here; a bandwidth-ascending sort in the selector is a one-liner if we later want hls.js-style ordering.

Trade-offs / open questions:

• First selection/switching set only: CMAF permits multiple selection sets and multiple switching sets; fine for single-video-track HLS, generalizing is a follow-up.
• Adapter destroy-recreate vs. in-place source replacement is unresolved (source-replacement.md / engine-adapter-integration.md). The src re-wire exists solely to compensate for destroy-recreate; if that's resolved toward in-place, the projection collapses to a one-time constructor wire.

Test plan:

• spf: deriveVideoRenditions behavior (derive/skip-unchanged/clear); getVideoRenditions selector.
• core: projection read/write/events, active reflection, frameRate → number, rebuild-on-set-change, re-wire-on-src, destroy.
• Full core dom/media (338) + spf engine/behaviors (417) green; typecheck, lint, check:workspace clean.

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Note

Medium Risk
Touches playback quality selection and DOM track projection with bidirectional sync; scope is bounded by tests and mirrors existing patterns, but wrong wiring could affect ABR or UI selection state.

Overview
SimpleHlsMedia now exposes the standard videoTracks / videoRenditions surface (read, write, events) so quality UIs can bind without adapter-specific APIs, aligned with the Hls.js media path.

On the SPF HLS engine, a new deriveVideoRenditions behavior (patterned after deriveCdnPriority) derives selectable quality levels from the resolved presentation’s first video switching set into a videoRenditions signal, clears on unload, and skips redundant signal writes when a reload keeps the same rendition ids. getVideoRenditions in track-selection utilities performs the presentation → VideoRenditionInfo mapping.

In core, SimpleHlsMediaMediaTracksMixin subscribes to that signal, builds one main track with a VideoRendition per level (including FrameRate → numeric frame rate), reflects active playback and selected manual pin from engine state, and maps videoRenditions.selectedIndex to userVideoTrackSelection ({ id } pins a level; -1 clears for ABR). Subscriptions re-wire on each src change because the adapter recreates the engine per assignment.

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