feat: 操作日志系统 + 日期修复 + 协同去重 + 主题持久化 + 计划自动完成

本次累积提交包含以下功能：

1. 修复：el-date-picker 缺失 value-format 导致日期保存偏移（8处）
2. 新增：协同拜访 visit_group_id 去重机制（完整副本 + 周报合并 + 亮灯去重）
3. 新增：计划自动完成（创建计划检测已有拜访 / 编辑拜访触发）
4. 新增：拜访表单选择客户后自动预填过期计划内容
5. 新增：移动端主题切换按钮 + 后端持久化
6. 新增：操作日志系统 (audit_logs)，全覆盖 8 个模块 CRUD
7. 新增：PC端「我的数据」支局长/领导视角客户经理列

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

backend/app/api/users.py

@@ -7,6 +7,7 @@ from sqlalchemy import select
 from app.database import get_db
 from app.middleware.auth import get_current_user, require_director
 from app.models.user import User
+from app.utils.audit import log_audit
 from app.schemas.customer import UserOut
 
 router = APIRouter(prefix="/users", tags=["Users"])
@@ -78,6 +79,9 @@ async def update_user_role(
         user.color = data.color
     await db.commit()
     await db.refresh(user)
+    # Audit log
+    await log_audit(db, "user", uuid.UUID(user_id), user.name, "update", current_user["user_id"], current_user["name"], f"角色更新为 {data.role}")
+    await db.commit()
 
     return {
         "id": str(user.id),
@@ -143,6 +147,32 @@ async def delete_user(
     if not user:
         raise HTTPException(status_code=404, detail="User not found")
 
+    user_name = user.name
     await db.delete(user)
     await db.commit()
-    return {"detail": "deleted", "name": user.name}
+    # Audit log
+    await log_audit(db, "user", uuid.UUID(user_id), user_name, "delete", current_user["user_id"], current_user["name"])
+    await db.commit()
+    return {"detail": "deleted", "name": user_name}
+
+
+class UpdateThemeRequest(BaseModel):
+    theme: str  # editorial / light
+
+
+@router.put("/me/theme")
+async def update_my_theme(
+    data: UpdateThemeRequest,
+    current_user: dict = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Update the current user's theme preference."""
+    if data.theme not in ("editorial", "light"):
+        raise HTTPException(status_code=400, detail="Invalid theme")
+    result = await db.execute(select(User).where(User.id == uuid.UUID(current_user["user_id"])))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+    user.theme = data.theme
+    await db.commit()
+    return {"theme": user.theme}