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/dto.test.ts

@@ -7,6 +7,7 @@ function item(username: string, opts: { pinnedAt?: string; isPlaying?: boolean;
     track: { id: 't', title: 't', artist: 'a', album: null, artworkUrl: null, durationMs: null, isrc: null, links: {} },
     isPlaying: opts.isPlaying ?? false,
     source: 'spotify',
+    sourceApp: null,
     progressMs: null,
     updatedAt: opts.updatedAt ?? '2026-01-01T00:00:00.000Z',
     pinnedAt: opts.pinnedAt ?? null,