WebPlayerViewComponent remounts the engine component for every playback
application, and the DOM Fullscreen API exits the moment its element leaves
the document. The fullscreen element was the engine shell, so every next-
episode click, autoplay hand-off, channel zap and alternative-source switch
dropped the viewer back to the page.
app-player-controls gains a `fullscreenTarget` input; HTML5, Video.js,
ArtPlayer and Embedded MPV forward it, and WebPlayerViewComponent passes its
own host element, which spans all applications of one mount. Keeping
fullscreen exposed a latent bug: the Electron header handoff set plain
fields under OnPush hosts and was only rendered thanks to the fullscreen
exit's stage resize; `channel`/`vjsOptions` are signals now.
Covered by unit regressions (fullscreen target, WebPlayerView remount, OnPush
handoff), a web-e2e run through a manual and an automatic episode switch, and
a manual Electron check. Docs and release note updated.
Closes#1498
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
