feat(anime): queue episodes to play next across anime

- Episode rows gain Play/Queue actions (and matching context-menu items); queued rows show their place in line, with a queue count and Clear queue in the episode header
- Queue lives in the main process (`anime-browser-queue.ts`) so it survives the browser window closing and advances on mpv's end-file even when nobody is watching; streams resolve at play time so a signed URL cannot expire while queued
- Holds mpv's keep-open off while the queue waits and restores it once empty; queueing with nothing playing just plays immediately
- Adds anime-browser-queue and episode-queue unit tests, IPC channels/contracts, and doc updates

src/animeui/detail-panel.ts

@@ -96,5 +96,7 @@ export function createDetailPanel({ api, setStatus }: DetailPanelOptions) {
     open,
     close,
     isOpen: (): boolean => !detail.classList.contains('hidden'),
+    /** The queue outlives the open anime, so it is pushed in from outside. */
+    setQueue: episodeList.setQueue,
   };
 }