baseline: Clover 独立仓库首次基线提交

将 Clover 从上层产品包旧仓库中独立出来,建立专属版本控制。
当前状态=纵切片端到端已打通(登录→选品→出文出图→审核→下载包),
M1文案质量去套路化已验收。此提交作为后续按核销清单逐条修复的基线。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/core/database.py

@@ -0,0 +1,53 @@
+"""
+app/core/database.py — SQLAlchemy 双库连接（MySQL + MongoDB）
+"""
+
+from motor.motor_asyncio import AsyncIOMotorClient
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, sessionmaker
+
+from app.core.config import get_settings
+
+settings = get_settings()
+
+# ── MySQL（主业务库）──────────────────────────────────
+engine = create_engine(
+    settings.DATABASE_URL,
+    pool_pre_ping=True,
+    pool_size=10,
+    max_overflow=20,
+    echo=(settings.APP_ENV == "development"),
+)
+
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+class Base(DeclarativeBase):
+    """所有 ORM 模型的基类。"""
+    pass
+
+
+def get_db():
+    """FastAPI 依赖注入：获取 DB Session，用完自动关闭。"""
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+# ── MongoDB（只存 AI debug trace，业务不依赖）──────────
+_mongo_client: AsyncIOMotorClient | None = None
+
+
+def get_mongo_client() -> AsyncIOMotorClient:
+    global _mongo_client
+    if _mongo_client is None:
+        _mongo_client = AsyncIOMotorClient(settings.MONGO_URI)
+    return _mongo_client
+
+
+def get_mongo_db():
+    """获取 MongoDB 数据库实例（clover_trace）。"""
+    client = get_mongo_client()
+    return client["clover_trace"]