Song progress bar, and poll right after a track ends

- Feed and profile cards show a progress bar with elapsed/total time, only
  when the source reports a real position (Plex, Jellyfin, the Android
  reader). It ticks locally between updates. Apple Music's guessed
  position is no longer reported.
- The Android reader advances MediaSession's stale position to now, stamps
  when it was read (the server corrects for upload delay), and reports
  seeks. The server pushes an update to watchers when a position jumps.
- When a polled source says where in the song someone is, the next poll is
  scheduled just after the song ends (never sooner than 5s), instead of
  waiting out the full interval.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8

apps/api/src/services/nowPlaying.ts

@@ -94,6 +94,8 @@ export async function publishNowPlaying(userId: string) {
   if (dto) await redis.publish(nowPlayingChannel(userId), JSON.stringify(dto));
 }
 
+const SEEK_THRESHOLD_MS = 5_000;
+
 /** Apply one provider's poll result to the user's now-playing state. Returns whether they're playing. */
 export async function applyPollResult(
   userId: string,
@@ -119,6 +121,13 @@ export async function applyPollResult(
 
   const track = await upsertTrack(result.track);
   const changed = !current || current.trackId !== track.id || !current.isPlaying;
+  // Same song, but not where it should be by now: a seek (or a restart). Tell
+  // watchers, or their progress bars would drift.
+  const jumped =
+    !changed &&
+    current.progressMs != null &&
+    result.progressMs != null &&
+    Math.abs(result.progressMs - (current.progressMs + (now.getTime() - current.updatedAt.getTime()))) > SEEK_THRESHOLD_MS;
   const newPlay =
     !current || current.trackId !== track.id || (!current.isPlaying && now.getTime() - current.updatedAt.getTime() > REPLAY_GAP_MS);
   const values = {
@@ -137,6 +146,7 @@ export async function applyPollResult(
     .onConflictDoUpdate({ target: schema.nowPlaying.userId, set: values });
 
   if (newPlay) await recordListen(userId, track.id, source, now);
+  if (jumped) await publishNowPlaying(userId);
   if (changed) {
     await publishNowPlaying(userId);
     const [t] = await db