M7 DONE via delegation — pv.youtube plays HD with audio

After hitting the segment-timing wall on our hand-rolled DASH MPD
(audio drifted -25s -> -44s behind video on long content), pivoted to
delegating playback to plugin.video.youtube v7.4.3 which already has
years of sidx-parsed SegmentTimeline + multi-client fallback work.

torttube._play() now:
  1. Tries _delegate_to_pv_youtube(yt_id) — sets a resolved URL of
     'plugin://plugin.video.youtube/play/?video_id=<id>'. Kodi
     chain-resolves to pv.youtube which builds the proper MPD and
     hands inputstream.adaptive a correctly-aligned manifest. Default.
  2. Falls back to our DASH builder (still in code, gated by
     'dash_enabled' setting + dash.on marker) if pv.youtube is absent.
  3. Falls through to yt-dlp progressive 360p as the final safety net.

When delegating, we skip our SponsorBlock monitor — pv.youtube has its
own and would double-skip otherwise.

Verified live on a LibreELEC Pi: LTT 'Trump Phone' (which crashed
our DASH with audio sync errors growing to -44s) now plays HD with
audio synced. 'Please sign in' message in log is from the tv_unplugged
Innertube client; pv.youtube falls back to a working client
automatically — no user account required.

Settings: prefer_pv_youtube boolean (default true). Addon v0.0.11.
Reference: https://kodi.wiki/view/Add-on:YouTube

MILESTONES.md

@@ -86,7 +86,30 @@
       progressive) is deprecated by YouTube; higher quality needs DASH
       manifest generation. Code path exists, gated behind `TORTTUBE_DASH=1`.
 
-## M7 — DASH / HD playback [WIP — close on segment timing]
+## M7 — HD playback [DONE via delegation]
+
+**Strategy pivoted 2026-05-23.** After hitting a wall on segment-timing
+alignment in our hand-rolled DASH MPD (audio drifted -25s → -44s behind
+video on long-form content), pivoted to delegating playback to the
+already-installed `plugin.video.youtube` v7.4.3. They already have
+years of sidx-parsed-SegmentTimeline + multi-client fallback work.
+Our delegation:
+
+- `_play()` first calls `_delegate_to_pv_youtube(yt_id)` which sets
+  `plugin://plugin.video.youtube/play/?video_id=<id>` via setResolvedUrl
+- Kodi chain-resolves to pv.youtube, which builds the proper MPD
+- inputstream.adaptive plays 1080p H.264 cleanly, audio in sync
+- Multi-client Innertube fallback handles "Please sign in" rejection
+  on the `tv_unplugged` client — succeeds on the next client without
+  needing the user to link an account
+
+Verified live on a LibreELEC Pi 2026-05-23 — LTT 'Trump Phone' video
+played at 1080p with audio, fullscreen.
+
+Settings: `prefer_pv_youtube` (default true). Disable to fall through
+to our native DASH/progressive paths.
+
+## M7-rejected — native DASH builder [PARKED]
 
 - [x] sidecar `resolve_dash` op returns rustypipe's full
       `video_only_streams` + `audio_streams` arrays (16+ representations)