fix: 修复 CI 流水线后端 lint 和 Django check 失败问题

- Backend Lint: 改用 uvx ruff 避免安装全部重型依赖（torch 等）
- Django Check: settings.py 读取 DB_ENGINE 环境变量，CI 使用 SQLite
- Django Check: 补充所有缺失的环境变量（Redis/Celery/DB）

Author: RMA-MUN

.github/workflows/ci.yml

@@ -18,10 +18,8 @@ jobs:
       - uses: astral-sh/setup-uv@v5
         with:
           python-version: "3.12"
-      - name: Install dependencies
-        run: uv sync --group dev
       - name: Run ruff
-        run: uv run ruff check .
+        run: uvx ruff check .
 
   frontend-build:
     name: Frontend Build
@@ -53,12 +51,18 @@ jobs:
         with:
           python-version: "3.12"
       - name: Install dependencies
-        run: uv sync
+        run: uv sync --no-build-isolation
       - name: Django check
         run: uv run python manage.py check --deploy
         env:
           DJANGO_SETTINGS_MODULE: DjangoUserService.settings
           JWT_SECRET_KEY: ci-test-key
           DB_ENGINE: django.db.backends.sqlite3
-          DB_NAME: db.sqlite3
-          CELERY_TASK_ALWAYS_EAGER: "True"
+          DB_NAME: ci_db.sqlite3
+          DB_USER: ""
+          DB_PASSWORD: ""
+          DB_HOST: ""
+          DB_PORT: ""
+          REDIS_CACHE_URL: redis://localhost:6379/1
+          CELERY_BROKER_URL: redis://localhost:6379/0
+          CELERY_RESULT_BACKEND: redis://localhost:6379/0

DjangoUserService/DjangoUserService/settings.py

@@ -100,20 +100,23 @@
 
 DATABASES = {
     'default': {
-        'ENGINE': 'django.db.backends.mysql',
+        'ENGINE': os.getenv('DB_ENGINE', 'django.db.backends.mysql'),
         'NAME': os.getenv('DB_NAME'),
         'USER': os.getenv('DB_USER'),
         'PASSWORD': os.getenv('DB_PASSWORD'),
         'HOST': os.getenv('DB_HOST'),
         'PORT': os.getenv('DB_PORT'),
-        'OPTIONS': {
-            'charset': 'utf8mb4',
-            'use_unicode': True,
-            'init_command': 'SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci',
-        },
     }
 }
 
+# MySQL 特有配置（非 SQLite 时使用）
+if DATABASES['default']['ENGINE'] != 'django.db.backends.sqlite3':
+    DATABASES['default']['OPTIONS'] = {
+        'charset': 'utf8mb4',
+        'use_unicode': True,
+        'init_command': 'SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci',
+    }
+
 # Celery 配置
 CELERY_BROKER_URL = os.getenv('CELERY_BROKER_URL')
 CELERY_RESULT_BACKEND = os.getenv('CELERY_RESULT_BACKEND')