ci: 添加 edict-backend CI job (PostgreSQL + Redis + Alembic)

新增 edict-backend job:
- PostgreSQL 16 + Redis 7 Service Containers
- 安装 edict/backend/requirements.txt 依赖
- edict/backend 下所有 .py 语法检查
- 运行 Alembic 数据库迁移验证
- 验证 FastAPI 应用可正常导入

.github/workflows/ci.yml

@@ -65,3 +65,59 @@ jobs:
           tags: edict:test
           cache-from: type=gha
           cache-to: type=gha,mode=max
+
+  edict-backend:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:16-alpine
+        env:
+          POSTGRES_DB: edict
+          POSTGRES_USER: edict
+          POSTGRES_PASSWORD: edict_dev_2024
+        ports:
+          - 5432:5432
+        options: >-
+          --health-cmd "pg_isready -U edict"
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 5
+      redis:
+        image: redis:7-alpine
+        ports:
+          - 6379:6379
+        options: >-
+          --health-cmd "redis-cli ping"
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 5
+    env:
+      DATABASE_URL: postgresql+asyncpg://edict:edict_dev_2024@localhost:5432/edict
+      REDIS_URL: redis://localhost:6379/0
+    steps:
+      - uses: actions/checkout@v6
+
+      - name: Set up Python 3.12
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+          cache: 'pip'
+          cache-dependency-path: edict/backend/requirements.txt
+
+      - name: Install backend dependencies
+        run: pip install -r edict/backend/requirements.txt
+
+      - name: Syntax check (py_compile)
+        run: |
+          find edict/backend -name '*.py' | while read f; do
+            echo "  checking $f"
+            python3 -m py_compile "$f"
+          done
+
+      - name: Run Alembic migrations
+        working-directory: edict
+        run: python -m alembic upgrade head
+
+      - name: Verify FastAPI app imports
+        working-directory: edict/backend
+        run: python -c "from app.main import app; print(f'FastAPI app loaded: {len(app.routes)} routes')"