Add phone playback reporting and pause sharing to the API

Phones that read system media sessions report playback themselves:
- POST /me/devices issues a per-phone token that can only call
  POST /devices/now-playing; revocable, hashed at rest, 10 per user
- Reports name the app ("via Spotify"); unknown apps use the OS label
- Push-reported playback expires after 9 minutes of silence, since
  phones send a heartbeat every 4 minutes while playing

Users can pause sharing (PUT /me/sharing: 1h, 8h, indefinitely). While
paused, connections aren't polled, phone reports are dropped, nothing is
added to history, and the current track switches to "played … ago".

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

packages/shared/src/time.ts

@@ -5,3 +5,11 @@ export function timeAgo(iso: string): string {
   if (s < 86400) return `${Math.floor(s / 3600)}h ago`;
   return `${Math.floor(s / 86400)}d ago`;
 }
+
+/** "until 5:30 PM", "until tomorrow 1:00 AM", or "until you turn it back on" for an indefinite pause. */
+export function pausedUntilLabel(iso: string, now = new Date()): string {
+  const until = new Date(iso);
+  if (until.getTime() - now.getTime() > 30 * 86_400_000) return 'until you turn it back on';
+  const time = until.toLocaleTimeString([], { hour: 'numeric', minute: '2-digit' });
+  return until.toDateString() === now.toDateString() ? `until ${time}` : `until tomorrow ${time}`;
+}