Add unit and integration test suites

- Shared: link building, feed ordering, input schemas, API client
- API unit: track matching, private-address blocking, token crypto,
  plan expiry, provider response parsing
- API integration against Postgres and Redis: auth, follows and pins,
  now-playing state, webhooks, OAuth return URLs, realtime, rate limits
- Tests use a dedicated *_test database and Redis DB, and refuse to wipe
  anything else; fetch is stubbed so they never hit the network
- Pin Node to 22.13+ (.nvmrc), which Vite's native bindings require

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

package.json

@@ -13,11 +13,13 @@
     "infra:down": "docker compose down",
     "db:generate": "npm run db:generate -w @musicshare/api",
     "db:migrate": "npm run db:migrate -w @musicshare/api",
-    "mobile": "npm run start -w @musicshare/mobile"
+    "mobile": "npm run start -w @musicshare/mobile",
+    "test": "turbo run test",
+    "lint": "turbo run lint"
   },
   "packageManager": "npm@10.8.1",
   "engines": {
-    "node": ">=22"
+    "node": ">=22.13"
   },
   "devDependencies": {
     "turbo": "^2.11.7",