feat: 初始化孕育无忧全栈项目基础代码结构

完成项目初始搭建，包含后端FastAPI+MongoDB服务、前端React+Vite项目的完整基础结构，添加各类配置文件与依赖清单，涵盖核心业务初始框架。

backend/app/database.py

@@ -0,0 +1,38 @@
+import os
+import certifi
+
+from beanie import init_beanie
+
+from app.config import settings
+from app.models.user import User
+from app.models.report import Report
+from app.models.analysis import Analysis
+from app.models.chat import ChatSession
+from app.models.checkup import CheckupPlan
+
+
+async def init_db():
+    use_mock = os.environ.get("USE_MONGOMOCK", "").lower() in ("1", "true", "yes")
+
+    if use_mock:
+        # 使用 mongomock 内存数据库（无需安装 MongoDB）
+        from mongomock_motor import AsyncMongoMockClient
+        client = AsyncMongoMockClient()
+    else:
+        from motor.motor_asyncio import AsyncIOMotorClient
+        # Only use TLS for Atlas (mongodb+srv://) connections
+        if settings.mongodb_url.startswith("mongodb+srv://") or "mongodb.net" in settings.mongodb_url:
+            client = AsyncIOMotorClient(settings.mongodb_url, tlsCAFile=certifi.where())
+        else:
+            client = AsyncIOMotorClient(settings.mongodb_url)
+
+    await init_beanie(
+        database=client[settings.mongodb_db_name],
+        document_models=[
+            User,
+            Report,
+            Analysis,
+            ChatSession,
+            CheckupPlan,
+        ],
+    )