feat: add WebDAV sync support and startup/shutdown scripts

Backend:
- Add uuid, sync_version, is_deleted fields to all syncable models
- Add SyncSettings model for WebDAV configuration (AES-256-GCM encrypted passwords)
- Add crypto.py: AES-256-GCM encryption derived from JWT_SECRET via PBKDF2
- Add sync_lock.py: thread-level sync lock with 503 middleware for write blocking
- Add webdav.py: WebDAV client using requests (PUT/GET/MKCOL/DELETE)
- Add sync_service.py: push/pull/bidirectional merge with LWW conflict resolution
- Add sync router with 8 endpoints: config, test, push, pull, sync, status, remote delete
- Add UUID backfill for existing records in init_db()
- Add SQLAlchemy before_update event to auto-increment sync_version
- Register sync middleware to block writes during sync (503)

Frontend:
- Add sync API client (WebUI/src/api/sync.ts)
- Add useSyncStore with config, test, push/pull/sync operations
- Add WebDAV config + sync UI in SettingsView
- Add 503 status code handling in axios interceptor
- Add uuid field to all TypeScript type definitions

Scripts:
- Add scripts/start.bat and scripts/stop.bat for project management

Design doc: docs/plan/webdav-sync-design.md

api/app/schemas/anniversary.py

@@ -54,6 +54,7 @@ class AnniversaryCategoryUpdate(BaseModel):
 class AnniversaryCategoryResponse(AnniversaryCategoryBase):
     """纪念日分类响应模型"""
     id: int
+    uuid: Optional[str] = None
 
     class Config:
         from_attributes = True
@@ -111,6 +112,7 @@ class AnniversaryUpdate(BaseModel):
 class AnniversaryResponse(AnniversaryBase):
     """纪念日响应模型"""
     id: int
+    uuid: Optional[str] = None
     created_at: datetime
     updated_at: datetime
     category: Optional[AnniversaryCategoryResponse] = None

api/app/schemas/category.py

@@ -1,4 +1,5 @@
 from pydantic import BaseModel, Field
+from typing import Optional
 
 
 class CategoryBase(BaseModel):
@@ -23,6 +24,7 @@ class CategoryUpdate(BaseModel):
 class CategoryResponse(CategoryBase):
     """分类响应模型"""
     id: int
+    uuid: Optional[str] = None
 
     class Config:
         from_attributes = True

api/app/schemas/goal.py

@@ -36,6 +36,7 @@ class GoalStepUpdate(BaseModel):
 
 class GoalStepResponse(GoalStepBase):
     id: int
+    uuid: Optional[str] = None
     goal_id: int
     reached_at: Optional[datetime] = None
     created_at: datetime
@@ -54,6 +55,7 @@ class GoalReviewCreate(BaseModel):
 
 class GoalReviewResponse(BaseModel):
     id: int
+    uuid: Optional[str] = None
     goal_id: int
     content: str
     rating: Optional[int] = None
@@ -97,6 +99,7 @@ class GoalUpdate(BaseModel):
 
 class GoalListResponse(GoalBase):
     id: int
+    uuid: Optional[str] = None
     progress: int
     completed_at: Optional[datetime] = None
     created_at: datetime

api/app/schemas/habit.py

@@ -29,6 +29,7 @@ class HabitGroupUpdate(BaseModel):
 class HabitGroupResponse(HabitGroupBase):
     """习惯分组响应模型"""
     id: int
+    uuid: Optional[str] = None
 
     class Config:
         from_attributes = True
@@ -68,6 +69,7 @@ class HabitUpdate(BaseModel):
 class HabitResponse(HabitBase):
     """习惯响应模型"""
     id: int
+    uuid: Optional[str] = None
     is_archived: bool
     created_at: datetime
     updated_at: datetime
@@ -87,6 +89,7 @@ class CheckinCreate(BaseModel):
 class CheckinResponse(BaseModel):
     """打卡记录响应模型"""
     id: int
+    uuid: Optional[str] = None
     habit_id: int
     checkin_date: date
     count: int

api/app/schemas/sync.py

@@ -0,0 +1,50 @@
+from pydantic import BaseModel, Field
+from typing import Optional
+from datetime import datetime
+
+
+class SyncConfigBase(BaseModel):
+    webdav_url: Optional[str] = None
+    webdav_username: Optional[str] = None
+    webdav_password: Optional[str] = None
+    webdav_path: str = "/elysia-todo/"
+    auto_sync: bool = False
+    auto_sync_interval: int = Field(default=300, ge=60)
+
+
+class SyncConfigUpdate(SyncConfigBase):
+    webdav_url: Optional[str] = None
+    webdav_username: Optional[str] = None
+    webdav_password: Optional[str] = None
+
+
+class SyncConfigResponse(BaseModel):
+    webdav_url: Optional[str] = None
+    webdav_username: Optional[str] = None
+    webdav_password: Optional[str] = None
+    webdav_path: str = "/elysia-todo/"
+    sync_enabled: bool = False
+    auto_sync: bool = False
+    auto_sync_interval: int = 300
+    last_sync_at: Optional[datetime] = None
+    last_sync_version: int = 0
+
+    class Config:
+        from_attributes = True
+
+
+class SyncStatusResponse(BaseModel):
+    syncing: bool
+    last_sync_at: Optional[datetime] = None
+    last_sync_version: int = 0
+    sync_enabled: bool = False
+
+
+class SyncTestResponse(BaseModel):
+    success: bool
+    message: str
+
+
+class SyncOperationResponse(BaseModel):
+    success: bool
+    message: str

api/app/schemas/tag.py

@@ -1,4 +1,5 @@
 from pydantic import BaseModel, Field
+from typing import Optional
 
 
 class TagBase(BaseModel):
@@ -14,6 +15,7 @@ class TagCreate(TagBase):
 class TagResponse(TagBase):
     """标签响应模型"""
     id: int
+    uuid: Optional[str] = None
 
     class Config:
         from_attributes = True

api/app/schemas/task.py

@@ -75,6 +75,7 @@ class TaskUpdate(BaseModel):
 class TaskResponse(TaskBase):
     """任务响应模型"""
     id: int
+    uuid: Optional[str] = None
     is_completed: bool
     created_at: datetime
     updated_at: datetime