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

turbo.json

@@ -7,10 +7,23 @@
     },
     "build": {
       "dependsOn": ["^build"],
+      "env": ["NEXT_PUBLIC_*", "EXPO_PUBLIC_*"],
       "outputs": [".next/**", "!.next/cache/**", "dist/**"]
     },
     "typecheck": {
       "dependsOn": ["^typecheck"]
+    },
+    "lint": {},
+    "transit": {
+      "dependsOn": ["^transit"]
+    },
+    "test": {
+      "dependsOn": ["transit"],
+      "env": ["TEST_DATABASE_URL", "TEST_REDIS_URL"]
+    },
+    "test:watch": {
+      "cache": false,
+      "persistent": true
     }
   }
 }