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/models/checkup.py

@@ -0,0 +1,30 @@
+from datetime import datetime, timezone
+from typing import Optional
+
+from beanie import Document, PydanticObjectId
+from pydantic import BaseModel, Field
+
+
+class CheckupItem(BaseModel):
+    title: str
+    week: int
+    date: Optional[str] = None
+    items: list[str] = Field(default_factory=list)
+    preparations: list[str] = Field(default_factory=list)
+    notes: str = ""
+    status: str = "upcoming"  # upcoming / completed / missed
+    importance: str = "medium"  # high / medium / low
+    report_ids: list[str] = Field(default_factory=list)  # linked report IDs
+
+
+class CheckupPlan(Document):
+    user_id: PydanticObjectId
+    checkups: list[CheckupItem] = Field(default_factory=list)
+    created_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+    updated_at: datetime = Field(default_factory=lambda: datetime.now(timezone.utc))
+
+    class Settings:
+        name = "checkup_plans"
+        indexes = [
+            "user_id",
+        ]