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/schemas.ts

@@ -47,3 +47,7 @@ export const jellyfinConnectSchema = z.object({
   username: z.string().trim().min(1).max(128),
   password: z.string().max(256).default(''),
 });
+
+/** Pause sharing: for an hour, until tomorrow, until turned back on, or resume (null). */
+export const PAUSE_OPTIONS = ['1h', '8h', 'indefinitely'] as const;
+export const setSharingSchema = z.object({ pause: z.enum(PAUSE_OPTIONS).nullable() });