docs(player): correct the stale "native video defaults to off" comments

DR-161 made `experimentalNativeVideo` default to on, but three comments still
described the pre-flip world and one of them was load-bearing:

- `nativeVideo.ts` labelled the store "Default off" directly above a `load()`
  that returns true when nothing is stored.
- The two PiP comments explained themselves as "what makes PiP work in the
  shipping configuration", which stopped being true when Android started
  shrinking the real ExoPlayer surface. They still describe the Linux path and
  the flag-off case, so they say that instead.
- `video_audio_codecs` justified its narrow codec list with "video does not play
  through ExoPlayer", which is no longer so on Android. The narrow list is still
  right, for a different reason now recorded: the flag is a user setting and a
  download outlives it, so only the intersection holds on both sides of the
  switch. DR-171 carries the same caveat.

No behaviour change.

src-tauri/src/repository/device_profile.rs

@@ -65,10 +65,18 @@ const FALLBACK_AUDIO_CODEC: &str = "aac";
 /// play the **video** can decode.
 ///
 /// The platform list comes from `MediaCodecList`, which describes ExoPlayer —
-/// but video does not play through ExoPlayer. Both Android and Linux render it
-/// in a webview `<video>` element, and Chromium/WebKit decode a much smaller set
-/// than the platform does. Advertising the raw list makes Jellyfin direct-play a
-/// track the webview cannot decode, and the user gets picture with no sound.
+/// but the webview `<video>` element may be what renders the video, and
+/// Chromium/WebKit decode a much smaller set than the platform does. Advertising
+/// the raw list makes Jellyfin direct-play a track the webview cannot decode, and
+/// the user gets picture with no sound.
+///
+/// Which renderer gets it is not fixed: Linux is always the element, and Android
+/// follows `experimentalNativeVideo`, which took ExoPlayer as its default in
+/// DR-161 but is a user setting either way. So the *narrow* list is the only one
+/// that holds on both sides of that switch. The cost is a Dolby-licensed Android
+/// device transcoding an E-AC-3 track its ExoPlayer could have direct-played;
+/// the alternative is silence for everyone the switch lands the other way, which
+/// is the bug this exists to prevent.
 ///
 /// The gap is widest on devices whose vendor licenses Dolby: a phone with
 /// `c2.dolby.eac3.decoder` reports `eac3`, so it — and only it — gets a silent