Merge branch 'main' into exp/orbit (pre-PR sync)

Conflicts resolved in:
- src/pages/SearchResults.tsx
- src/pages/AdvancedSearch.tsx

Both pages were rewritten on main (PR #303) to use the shared
<SongRow> component with click-to-enqueueAndPlay semantics. Orbit's
playSong helper that branched on orbit-active is no longer needed
at the page level — instead, orbit awareness moved INTO SongRow and
SongCard themselves: in an active orbit session both buttons collapse
into addTrackToOrbit (suggest for guests, host-enqueue for the host)
so we don't ship a queue replacement to every guest.

Also kept main's IntersectionObserver-based pagination on both pages.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/utils/playSong.ts

@@ -0,0 +1,61 @@
+import { usePlayerStore, songToTrack } from '../store/playerStore';
+import type { SubsonicSong } from '../api/subsonic';
+
+function fadeOut(setVolume: (v: number) => void, from: number, durationMs: number): Promise<void> {
+  return new Promise(resolve => {
+    const steps = 16;
+    const stepMs = durationMs / steps;
+    let step = 0;
+    const id = setInterval(() => {
+      step++;
+      setVolume(Math.max(0, from * (1 - step / steps)));
+      if (step >= steps) {
+        clearInterval(id);
+        resolve();
+      }
+    }, stepMs);
+  });
+}
+
+/**
+ * Play a single song. When `queue` is provided, surrounds the chosen song with that queue
+ * so Next/Prev work — pass the rail / pool the click came from. Mirrors playAlbum's fade-out.
+ */
+export async function playSongNow(song: SubsonicSong, queue?: SubsonicSong[]): Promise<void> {
+  const track = songToTrack(song);
+  const tracks = queue && queue.length > 0
+    ? queue.map(songToTrack)
+    : [track];
+
+  const store = usePlayerStore.getState();
+  const { isPlaying, volume } = store;
+
+  if (isPlaying) {
+    await fadeOut(store.setVolume, volume, 700);
+    usePlayerStore.setState({ volume });
+  }
+
+  usePlayerStore.getState().playTrack(track, tracks);
+}
+
+/**
+ * Append the song to the existing queue (if not already there) and immediately jump to it.
+ * Existing queue stays intact — different from playSongNow which replaces the queue.
+ */
+export async function enqueueAndPlay(song: SubsonicSong): Promise<void> {
+  const track = songToTrack(song);
+  const store = usePlayerStore.getState();
+  const { isPlaying, volume, queue } = store;
+
+  if (isPlaying) {
+    await fadeOut(store.setVolume, volume, 700);
+    usePlayerStore.setState({ volume });
+  }
+
+  if (!queue.some(t => t.id === track.id)) {
+    usePlayerStore.getState().enqueue([track]);
+  }
+  // playTrack with no queue arg uses the current state.queue, finds the track by id,
+  // and sets queueIndex accordingly.
+  usePlayerStore.getState().playTrack(track);
+}