fix(playback): route MKV sources as Matroska (#1210)

* docs(playback): design native MKV source routing

* fix(playback): route MKV sources as Matroska

* chore(playback): address MKV review feedback

docs/architecture/embedded-inline-playback.md

@@ -264,6 +264,13 @@ The diagnostic surface covers the inline player viewport when playback fails, wi
 
 URL extension metadata is filtered before diagnostics and player selection use it. Web script extensions such as `.php` are not shown as stream containers; explicit media query metadata such as `extension=ts` or `format=m3u8` is preferred when present.
 
+MKV sources are attempted through Chromium's native Matroska path. Video.js
+receives `video/matroska` for `.mkv` URLs and explicit query metadata such as
+`extension=mkv` or `container=mkv`; ArtPlayer and HTML5 continue to use their
+native video paths. This is container support rather than a universal codec
+guarantee: native source or decode failures still produce the existing
+diagnostic and explicit MPV/VLC fallback.
+
 Portal VOD and episode payloads with `contentInfo` are treated as non-live by the inline players unless `isLive` is explicitly set. If Chromium leaves the underlying MediaSource duration at `Infinity` for a finite TS VOD, the Video.js wrapper normalizes its UI duration from the finite `seekable` or `buffered` range. Embedded MPV uses the same live decision rule and shows an unknown duration placeholder for VOD/episode snapshots until MPV reports a finite duration. This removes the misleading `LIVE` control state without changing stream decoding, diagnostics, or external fallback behavior.
 
 When a diagnostic is actionable in Electron, the diagnostic surface may offer `Open in MPV`, `Open in VLC`, `Copy URL`, technical details, and `Retry`. Web builds only expose copy/help text and retry. MPV/VLC fallback requests carry the original `ResolvedPortalPlayback` payload so headers, referer, origin, user-agent, content metadata, and resume offset stay intact. Retry clears the current diagnostic and rebuilds the active inline player inputs; it does not change the saved player setting.