Add CI: typecheck, lint, tests, migration drift, builds

Runs against Postgres and Redis service containers. Fails if schema.ts
changes without a generated migration, and bundles the mobile app for
iOS and Android to catch Metro resolution issues.

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

.github/workflows/ci.yml

@@ -0,0 +1,77 @@
+name: CI
+
+on:
+  push:
+    branches: [master, main]
+  pull_request:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    timeout-minutes: 20
+
+    services:
+      postgres:
+        image: postgres:17
+        env:
+          POSTGRES_USER: musicshare
+          POSTGRES_PASSWORD: musicshare
+          POSTGRES_DB: musicshare_test
+        ports: ['5432:5432']
+        options: >-
+          --health-cmd "pg_isready -U musicshare"
+          --health-interval 5s --health-timeout 5s --health-retries 10
+      redis:
+        image: redis:7
+        ports: ['6379:6379']
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 5s --health-timeout 5s --health-retries 10
+
+    env:
+      TEST_DATABASE_URL: postgres://musicshare:musicshare@localhost:5432/musicshare_test
+      TEST_REDIS_URL: redis://localhost:6379/1
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: .nvmrc
+          cache: npm
+
+      - run: npm ci
+
+      - name: Typecheck
+        run: npx turbo run typecheck
+
+      - name: Lint
+        run: npx turbo run lint
+
+      - name: Test
+        run: npx turbo run test
+
+      - name: Check migrations match the schema
+        working-directory: apps/api
+        run: |
+          npx drizzle-kit generate --name ci-check
+          if [ -n "$(git status --porcelain drizzle)" ]; then
+            echo "::error::schema.ts has changes without a migration. Run 'npm run db:generate' and commit the result."
+            git status --porcelain drizzle
+            exit 1
+          fi
+
+      - name: Build web
+        run: npx turbo run build --filter=@musicshare/web
+        env:
+          NEXT_PUBLIC_API_URL: https://api.example.com
+
+      - name: Bundle mobile (iOS + Android)
+        working-directory: apps/mobile
+        run: npx expo export --platform ios --platform android --output-dir /tmp/expo-export
+        env:
+          EXPO_PUBLIC_API_URL: https://api.example.com