ci: add pull request verification workflow

.github/workflows/pr-validation.yml

@@ -0,0 +1,54 @@
+name: PR Validation
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  frontend-check:
+    name: Frontend Build and Lint Validation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 18
+          cache: 'npm'
+          cache-dependency-path: frontend/package-lock.json
+
+      - name: Install Frontend Dependencies
+        run: npm ci
+        working-directory: frontend
+
+      - name: Lint Frontend
+        run: npm run lint
+        working-directory: frontend
+
+      - name: Build Frontend
+        run: npm run build
+        working-directory: frontend
+
+  backend-check:
+    name: Backend Syntax and Dependencies Validation
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 18
+          cache: 'npm'
+          cache-dependency-path: server/package-lock.json
+
+      - name: Install Backend Dependencies
+        run: npm ci
+        working-directory: server
+
+      - name: Verify Backend Entry Point Syntax
+        run: node --check server.js
+        working-directory: server