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/models/goal.py

@@ -1,4 +1,5 @@
-from sqlalchemy import Column, Integer, String, Text, Date, DateTime, ForeignKey, Table, desc
+import uuid as _uuid
+from sqlalchemy import Column, Integer, String, Text, Date, DateTime, Boolean, ForeignKey, Table, desc
 from sqlalchemy.orm import relationship
 from app.database import Base
 from app.utils.datetime import utcnow
@@ -18,6 +19,7 @@ class Goal(Base):
     __tablename__ = "goals"
 
     id = Column(Integer, primary_key=True, index=True)
+    uuid = Column(String(36), default=lambda: str(_uuid.uuid4()), unique=True, index=True)
     title = Column(String(200), nullable=False)
     description = Column(Text, nullable=True)
     status = Column(String(20), default="active")  # active/paused/completed/abandoned
@@ -28,6 +30,8 @@ class Goal(Base):
     color = Column(String(20), default="#FFB7C5")
     icon = Column(String(50), default="flag")
     sort_order = Column(Integer, default=0)
+    is_deleted = Column(Boolean, default=False)
+    sync_version = Column(Integer, default=1)
     created_at = Column(DateTime, default=utcnow)
     updated_at = Column(DateTime, default=utcnow, onupdate=utcnow)
 
@@ -51,6 +55,7 @@ class GoalStep(Base):
     __tablename__ = "goal_steps"
 
     id = Column(Integer, primary_key=True, index=True)
+    uuid = Column(String(36), default=lambda: str(_uuid.uuid4()), unique=True, index=True)
     goal_id = Column(Integer, ForeignKey("goals.id"), nullable=False)
     parent_id = Column(Integer, ForeignKey("goal_steps.id"), nullable=True)
     title = Column(String(200), nullable=False)
@@ -59,6 +64,8 @@ class GoalStep(Base):
     target_date = Column(Date, nullable=True)
     reached_at = Column(DateTime, nullable=True)
     sort_order = Column(Integer, default=0)
+    is_deleted = Column(Boolean, default=False)
+    sync_version = Column(Integer, default=1)
     created_at = Column(DateTime, default=utcnow)
 
     # 关联关系
@@ -71,9 +78,12 @@ class GoalReview(Base):
     __tablename__ = "goal_reviews"
 
     id = Column(Integer, primary_key=True, index=True)
+    uuid = Column(String(36), default=lambda: str(_uuid.uuid4()), unique=True, index=True)
     goal_id = Column(Integer, ForeignKey("goals.id"), nullable=False)
     content = Column(Text, nullable=False)
     rating = Column(Integer, nullable=True)  # 1-5 自评
+    is_deleted = Column(Boolean, default=False)
+    sync_version = Column(Integer, default=1)
     created_at = Column(DateTime, default=utcnow)
 
     # 关联关系