fix(anime): strip disguised HLS segments and report real playback errors

Some hosts prepend a fake image header (a real 1x1 PNG) to every HLS
segment; ffmpeg probes the segment as a picture and mpv drops back to
idle with no window while the browser claims the episode is playing.

- Route bridge-served m3u8 streams through a local strip proxy that
  scans each segment for the first genuine MPEG-TS packet run and drops
  the junk in front of it; playlists get absolute origins rewritten so
  segment requests come back through the proxy. Non-TS bodies pass
  through untouched.
- Only report ok from playEpisode once mpv configures a video output;
  an end-file with reason error surfaces mpv's own message (e.g. "no
  audio or video data played") in the browser status bar instead of
  "Playing". New end-file event plumbed through the mpv IPC client.

src/anime-bridge/playback-outcome.ts

@@ -0,0 +1,80 @@
+/**
+ * Confirms that a `loadfile` handed to mpv actually turned into playback.
+ *
+ * Sending the command proves nothing: mpv accepts the file, fails to decode it
+ * (a dead host, a disguised stream the proxy could not fix), fires `end-file`
+ * with reason "error", and drops back to `--idle` — with no window, because
+ * idle mpv shows none. The UI would happily say "Playing" over a blank desktop.
+ *
+ * Success is mpv configuring a video output (`vo-configured`), which is
+ * literally "a window with frames in it". `file-loaded` is not enough — the
+ * broken stream in the wild reached it before dying. Failure is an `end-file`
+ * with reason "error"; the end-file of the file being *replaced* arrives with
+ * "stop"/"redirect" and is ignored.
+ */
+
+export interface PlaybackEndFileEvent {
+  reason: string;
+  fileError: string | null;
+}
+
+export type PlaybackOutcome = { ok: true } | { ok: false; error: string };
+
+export interface WatchPlaybackOutcomeDeps {
+  /** Subscribe to mpv end-file events; returns the unsubscribe. */
+  onEndFile: (listener: (event: PlaybackEndFileEvent) => void) => () => void;
+  /** One-shot mpv property read; may reject while the file is still loading. */
+  readProperty: (name: string) => Promise<unknown>;
+  wait: (ms: number) => Promise<void>;
+  timeoutMs?: number;
+  probeIntervalMs?: number;
+}
+
+export interface PlaybackOutcomeWatch {
+  wait: () => Promise<PlaybackOutcome>;
+  dispose: () => void;
+}
+
+export const DEFAULT_PLAYBACK_OUTCOME_TIMEOUT_MS = 20_000;
+const DEFAULT_PROBE_INTERVAL_MS = 500;
+
+/**
+ * Call *before* sending `loadfile` so the error subscription cannot lose a
+ * race against a fast failure; await `wait()` after the commands went out.
+ */
+export function watchPlaybackOutcome(deps: WatchPlaybackOutcomeDeps): PlaybackOutcomeWatch {
+  const timeoutMs = deps.timeoutMs ?? DEFAULT_PLAYBACK_OUTCOME_TIMEOUT_MS;
+  const probeIntervalMs = deps.probeIntervalMs ?? DEFAULT_PROBE_INTERVAL_MS;
+
+  let failure: PlaybackOutcome | null = null;
+  const unsubscribe = deps.onEndFile((event) => {
+    if (event.reason !== 'error') return;
+    failure = {
+      ok: false,
+      error: event.fileError
+        ? `mpv could not play this stream: ${event.fileError}`
+        : 'mpv could not play this stream.',
+    };
+  });
+
+  async function wait(): Promise<PlaybackOutcome> {
+    for (let elapsed = 0; elapsed < timeoutMs; elapsed += probeIntervalMs) {
+      if (failure) return failure;
+      try {
+        if ((await deps.readProperty('vo-configured')) === true) return { ok: true };
+      } catch {
+        // The property is unreadable while mpv is between files; keep polling.
+      }
+      if (failure) return failure;
+      await deps.wait(probeIntervalMs);
+    }
+    return (
+      failure ?? {
+        ok: false,
+        error: 'Playback did not start. mpv gave no error; try another server or quality.',
+      }
+    );
+  }
+
+  return { wait, dispose: unsubscribe };
+}