Add API and worker: accounts, follows, now-playing, cross-service links

- Fastify API with cookie (web) and bearer (mobile) sessions, follows,
  pinned friends, featured songs, account deletion, Redis-backed rate limits
- Providers: Spotify (OAuth), Last.fm, ListenBrainz, Plex (PIN flow and
  server discovery), Jellyfin (token auth, revoked on disconnect)
- Worker polls on an adaptive schedule in a Redis sorted set, so polling
  scales horizontally and API usage tracks whether anyone is watching
- Track resolver links songs across services via ISRC (Deezer, Spotify),
  iTunes search and song.link
- Realtime updates over WebSocket fan out through Redis pub/sub
- User-supplied server URLs are restricted to public addresses, checked
  both up front and at connect time to defeat DNS rebinding

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

apps/api/src/lib/crypto.ts

@@ -0,0 +1,22 @@
+import { createCipheriv, createDecipheriv, createHash, randomBytes } from 'node:crypto';
+import { env } from '../env';
+
+const key = Buffer.from(env.TOKEN_ENCRYPTION_KEY, 'base64');
+
+/** AES-256-GCM. Output: base64(iv | tag | ciphertext). */
+export function encrypt(plaintext: string): string {
+  const iv = randomBytes(12);
+  const cipher = createCipheriv('aes-256-gcm', key, iv);
+  const ct = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
+  return Buffer.concat([iv, cipher.getAuthTag(), ct]).toString('base64');
+}
+
+export function decrypt(payload: string): string {
+  const buf = Buffer.from(payload, 'base64');
+  const decipher = createDecipheriv('aes-256-gcm', key, buf.subarray(0, 12));
+  decipher.setAuthTag(buf.subarray(12, 28));
+  return Buffer.concat([decipher.update(buf.subarray(28)), decipher.final()]).toString('utf8');
+}
+
+export const sha256 = (s: string) => createHash('sha256').update(s).digest('hex');
+export const randomToken = (bytes = 32) => randomBytes(bytes).toString('base64url');