feat(playback): embedded mpv pre-0.22 hardening, Linux parity, and localization (#1122)

* fix(playback): harden embedded mpv session handling and support detection

- guard the session controller against late startup rejections clobbering
  a newer session during fast channel zapping
- exclude the refresh timestamp from the session-update dedup key so idle
  sessions stop re-emitting IPC updates every 500 ms
- macOS: reconcile async loadfile replies by request id so a rejected
  seek/aid/speed on a live stream no longer flips the session to error
- append --ozone-platform=x11 on Linux in main.ts so direct binary and
  AppImage launches match the packaged .desktop launcher behavior
- return a sandbox-specific unsupported reason in Flatpak/Snap instead of
  asking the user to install mpv inside the sandbox
- update the stale "macOS only" embedded MPV claim in CLAUDE.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(playback): populate Linux audio tracks and fix ARM Linux packaging

- Linux poller now reads track-list/count each tick and walks the scalar
  track-list/N/* sub-properties when the count changes, so the audio-track
  menu is no longer empty; selection reconciles from the aid property
- afterPack replaces the x64 embedded_mpv.node with an
  embedded-mpv-unavailable.txt marker in arm64/armv7l Linux packages, and
  package-layout verification rejects foreign-architecture addons while
  requiring the marker
- extend native source invariants for the non-fatal async-reply rule
  (macOS) and the Linux track-list polling contract
- document the Linux track-list mechanics and ARM packaging behavior in
  docs/architecture/embedded-mpv-native.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* feat(playback): embedded mpv player UX polish and full localization

- click on the video toggles pause (same action as Space) with a 250 ms
  grace period so double-click fullscreen cancels the pending pause; no
  DOM overlay is drawn — the dock transport icon is the feedback
- timeline scrubbing previews the drag position locally and commits a
  single seek on release instead of one IPC seek per drag pixel
- translate all player UI strings (controls, tooltips, aria-labels,
  status and recording messages) via new EMBEDDED_MPV.PLAYER.* keys,
  synced across en + 17 locales through the i18n-fill workflow
- replace the legacy @Output() EventEmitter with the signal output() API

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(playback): react to language changes and respect ozone platform hint

Address review feedback on #1122:
- add a translationsTick signal (onLangChange/onTranslationChange/
  onDefaultLangChange) read by every computed() and template helper that
  calls translate.instant(), so labels re-evaluate on a runtime language
  switch and when the translation file finishes loading after mount
- suppress the Linux --ozone-platform=x11 fallback when the user set
  ELECTRON_OZONE_PLATFORM_HINT, matching the existing respect for an
  explicit --ozone-platform switch

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

docs/architecture/embedded-mpv-native.md

@@ -40,7 +40,9 @@ Linux native Wayland embedding is not implemented. When Electron is started on X
 
 ## Linux Support Matrix
 
-Embedded MPV on Linux is supported only for x64 desktop builds where Electron runs under X11 or Xwayland and an `mpv` executable is available on `PATH`. Native Wayland embedding is not supported in this implementation. Packaged Linux launchers pass `--ozone-platform=x11` so Wayland desktops use Xwayland when it is available.
+Embedded MPV on Linux is supported only for x64 desktop builds where Electron runs under X11 or Xwayland and an `mpv` executable is available on `PATH`. Native Wayland embedding is not supported in this implementation. Packaged Linux launchers pass `--ozone-platform=x11` so Wayland desktops use Xwayland when it is available, and `main.ts` appends the same switch on Linux when it is absent so direct binary/AppImage launches from a terminal behave like launcher starts. Explicit user intent is never overridden: both a user-provided `--ozone-platform` switch and the `ELECTRON_OZONE_PLATFORM_HINT` environment variable suppress the fallback.
+
+When the `mpv` executable probe fails inside a Flatpak or Snap sandbox (`FLATPAK_ID`/`SNAP` env present), the support reason explains that sandboxed packages cannot access a system mpv instead of asking the user to install it.
 
 Current release-announcement wording should stay close to this:
 
@@ -101,6 +103,8 @@ Subtitle tracks mirror the audio-track contract: same `track-list` source, same
 
 The renderer learns which features the loaded addon binary supports through the `EmbeddedMpvSupport.capabilities` field returned from `getEmbeddedMpvSupport()`. The service probes `typeof addon.<method> === 'function'` for each optional native export. Older addon binaries with the original audio-only surface return `capabilities: { subtitles: false, playbackSpeed: false, aspectOverride: false, screenshot: false, recording: false }`, and the renderer hides the corresponding controls instead of throwing at runtime. Linux intentionally does not export libmpv-only optional controls while it uses the process-isolated `mpv --wid` backend.
 
+Linux audio-track discovery works differently from macOS/Windows because the hand-rolled JSON IPC reply parser only understands scalar `data` values: the poll loop reads `track-list/count` every tick and walks the scalar `track-list/N/{type,id,title,lang,default,forced}` sub-properties only when the count changes. The selected track is reconciled from the scalar `aid` property on every tick (`aid` reads back non-numeric when audio is disabled, which maps to "no selection"). Track switching still goes through `set_property aid` over the same socket.
+
 ## Session End And Series Navigation
 
 `EmbeddedMpvSessionStatus` includes `ended` for successful EOF only. The native addon maps `MPV_EVENT_END_FILE` to:
@@ -113,6 +117,8 @@ The renderer learns which features the loaded addon binary supports through the
 
 Renderer autoplay must use `ended` only. It must not treat `closed`, `idle`, or `error` as a request to continue to the next episode.
 
+Async command/property replies are reconciled against pending request IDs on all platforms: only a failed `loadfile` reply (or a recording start/stop reply) may change the session status. A rejected seek, `aid`, or `speed` reply on a live stream records `snapshot.error` but must not flip a playing session to `error`, because playback continues.
+
 The native addon also observes mpv's `eof-reached` property and maps a true value to `ended`. This is required because embedded sessions run with `keep-open=yes`; MPV can pause at EOF while keeping the file loaded, so relying only on `MPV_EVENT_END_FILE` can leave the renderer in a paused-at-end state and block series autoplay.
 
 Series episode navigation is owned by the portal feature components and passed through the shared inline player to `EmbeddedMpvPlayerComponent`. The embedded MPV controls show `skip_previous` and `skip_next` buttons only for non-live series playback. The shared navigation payload contains `canPrevious`, `canNext`, and `autoplayEnabled`; the component disables previous/next at the current-season boundaries and guards the output handlers as well as the button disabled state.
@@ -198,6 +204,7 @@ Current development behavior:
 Current release caveat:
 
 - Release packaging requires a `vendored-lgpl` runtime manifest on macOS and Windows, and an `external-mpv-process` manifest on Linux.
+- The Linux addon is built once per CI host architecture (x64). Linux packages for other architectures (arm64, armv7l) must not ship that foreign addon: `afterPack` replaces the native directory with an `embedded-mpv-unavailable.txt` marker explaining that embedded MPV is not bundled for that architecture, and package-layout verification rejects a foreign-architecture `embedded_mpv.node` while requiring the marker.
 - macOS release packaging rejects embedded MPV binaries linked to `/opt/homebrew` or `/usr/local`.
 - Windows release packaging verifies that the platform runtime file is present when Embedded MPV is required. Linux release packaging verifies that the addon and manifest are present and that no bundled `libmpv.so` files slipped into the package.
 - Local development can opt into Homebrew `libmpv` only by setting `IPTVNATOR_EMBEDDED_MPV_ALLOW_HOMEBREW=1`; packaged release validation rejects that runtime origin.