feat(player): restore the last player session at boot

Reload the episode that was loaded in the player when the previous run
ended (persisted on play/load and synchronously at exit) into the Player
tab paused at its saved position — never autostarted. Episodes at or
above 98% completion are skipped, as are empty-player and unsubscribed
episodes.

- useAudio gains load(episode) (sets currentEpisode/position/Now Playing
  without starting the backend) and restoreLastSession(), triggered once
  at boot and serialized through a chain so a late-finishing boot restore
  can't clobber later state.
- togglePlayback branches on a startedPlayback flag: a restored episode
  starts the backend from the saved position; a paused one resumes.
- stop() clears the marker; the exit teardown writes it synchronously
  (process.exit bypasses async writes).
- feed/progress stores expose whenReady() so restore waits for the async
  boot loads; feed store gains findEpisode().
- app-persistence serializes last-player marker writes and exposes
  waitForLastPlayerWrite() for deterministic tests.
- tests/restore-session.test.ts: real modules + local RSS feed server;
  the real useAudio is imported via a ?restore-test query suffix to
  bypass the suite's mock.module leak across shared bun workers.

src/stores/feed.ts

@@ -409,9 +409,15 @@ function createFeedStore() {
 		}
 	};
 
+	// Resolves once the persisted feeds are loaded and visible to feeds() —
+	// before the background refresh so boot-time consumers (player-session
+	// restore) don't wait on the network.
+	const { promise: feedsReady, resolve: resolveFeedsReady } =
+		Promise.withResolvers<void>();
 	(async () => {
 		const loadedFeeds = await loadFeedsFromFile();
 		if (loadedFeeds.length > 0) setFeeds(loadedFeeds);
+		resolveFeedsReady();
 		const loadedSources = await loadSourcesFromFile<PodcastSource>();
 		// The default "rss" placeholder source fabricated fake search results
 		// and was removed from DEFAULT_SOURCES; drop it from persisted configs
@@ -565,6 +571,16 @@ function createFeedStore() {
 		return feeds().find((f) => f.id === feedId);
 	};
 
+	/** Find an episode by ID across all loaded feeds (undefined when the
+	 *  episode isn't in any loaded window, e.g. an unsubscribed show). */
+	const findEpisode = (episodeId: string): Episode | undefined => {
+		for (const feed of feeds()) {
+			const ep = feed.episodes.find((e) => e.id === episodeId);
+			if (ep) return ep;
+		}
+		return undefined;
+	};
+
 	/** Get selected feed */
 	const getSelectedFeed = (): Feed | undefined => {
 		const id = selectedFeedId();
@@ -670,10 +686,15 @@ function createFeedStore() {
 		selectedFeedId,
 		isLoadingMore,
 
+		/** Resolves once persisted feeds are loaded from disk (before the
+		 *  background refresh). */
+		whenReady: () => feedsReady,
+
 		// Computed
 		getFilteredFeeds,
 		getAllEpisodesChronological,
 		getFeed,
+		findEpisode,
 		getSelectedFeed,
 		hasMoreEpisodes,
 		isLoadingFeeds,

src/stores/progress.ts

@@ -53,11 +53,17 @@ async function initProgress(): Promise<void> {
 	setProgressMap(parsed);
 }
 
-// Fire-and-forget init
-initProgress();
+// Fire-and-forget init; the promise is exposed via whenReady() so boot-time
+// consumers (e.g. player-session restore) can await the file load.
+const progressInit = initProgress();
 
 function createProgressStore() {
 	return {
+		/**
+		 * Resolves once the persisted progress map has been loaded from disk.
+		 */
+		whenReady: () => progressInit,
+
 		/**
 		 * Get progress for a specific episode.
 		 */