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.test.ts

@@ -1,5 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
-import { timeAgo } from './time';
+import { pausedUntilLabel, timeAgo } from './time';
 
 describe('timeAgo', () => {
   beforeEach(() => {
@@ -18,3 +18,14 @@ describe('timeAgo', () => {
     expect(timeAgo(iso)).toBe(expected);
   });
 });
+
+describe('pausedUntilLabel', () => {
+  const now = new Date(2026, 9, 3, 14, 0);
+  it('says "until you turn it back on" for indefinite pauses', () => {
+    expect(pausedUntilLabel(new Date(2126, 0, 1).toISOString(), now)).toBe('until you turn it back on');
+  });
+  it('shows a time for today and "tomorrow" past midnight', () => {
+    expect(pausedUntilLabel(new Date(2026, 9, 3, 15, 0).toISOString(), now)).toMatch(/^until \d/);
+    expect(pausedUntilLabel(new Date(2026, 9, 4, 1, 0).toISOString(), now)).toMatch(/^until tomorrow /);
+  });
+});