feat(playback): fullscreen episode panel for series playback (#1620)

Series playing in fullscreen get the same slide-in side panel the live channel list has, with season tabs and the episode list: rest the mouse on the left edge, click it, or press C; pick an episode and it plays inline without leaving fullscreen.

- Panel contract: `FullscreenChannelPanelHost` gains optional `panelSearchEnabled` and `panelKind`; the template context gains `open`. Pointer/keyboard rules and the four live providers are unchanged.
- Series host: `PortalInlinePlayerComponent` provides the token through `createEpisodePanelHost()` and stamps `app-fullscreen-episode-panel` (SeasonTabsComponent over rows with TMDB still or numeral tile, label, runtime, clamped overview, progress, watched check, now-playing marker; playing row centred on open). Episode clicks reuse the Up Next rail's inline path; season tab clicks reach the hosts' `onSeasonSelected` (Xtream TMDB season enrichment, Stalker lazy VOD load with a Retry row after a failed request).
- Gates: `Settings.fullscreenChannelPanel` (label now covers both lists in all locales), episode content only, native-view Embedded MPV withheld by the view, external players excluded.
- Inline-series e2e moved to `xtream-series-playback.e2e.ts` with shared Xtream helpers in a fixture; adds a fullscreen episode switch through the panel.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.changes/playback-fullscreen-episode-panel.md

@@ -0,0 +1,7 @@
+---
+type: feature
+area: playback
+highlight: Episode list in fullscreen
+---
+
+Series playback now has the slide-in list in fullscreen too: rest the mouse on the left edge, click it, or press C to see the season tabs and episodes with stills, runtimes, descriptions and watch progress, and jump to another episode without leaving fullscreen. Works for Xtream and Stalker series with any built-in player.