ci: add GitHub Actions CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,104 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  # ─── Listener (Node.js + TypeScript + Jest) ───────────────────────────────
+  listener:
+    name: Listener — typecheck, lint, test
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: listener
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+          cache-dependency-path: listener/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Typecheck
+        run: npm run typecheck
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Format check
+        run: npm run format:check
+
+      - name: Test
+        run: npm test -- --ci --runInBand
+
+  # ─── Dashboard (React + Vite + Jest) ──────────────────────────────────────
+  dashboard:
+    name: Dashboard — typecheck, lint, test, build
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: dashboard
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+          cache-dependency-path: dashboard/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Format check
+        run: npm run format:check
+
+      - name: Test
+        run: npm test -- --ci
+
+      - name: Build
+        run: npm run build
+
+  # ─── Frontend (React + Vite + Vitest) ─────────────────────────────────────
+  frontend:
+    name: Frontend — typecheck, lint, test, build
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: frontend
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+          cache-dependency-path: frontend/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Test
+        run: npm test
+
+      - name: Build
+        run: npm run build