feat: Enhance models and README with additional features and improvements

- Updated README to include KodBox in project vision.
- Added model descriptions for clarity in Download, File, Folder, Group, Node, Order, Policy, Redeem, Report, Request, Response, Setting, Share, SourceLink, StoragePack, Tag, Task, User, and WebDAV.
- Changed optional fields from Optional[...] to the new union type syntax (e.g., str | None).
- Improved foreign key references in models for consistency.
- Refactored relationships in models to use singular forms where appropriate.
- Updated login service to reflect changes in request model types.

models/webdav.py

@@ -7,17 +7,18 @@ if TYPE_CHECKING:
     from .user import User
 
 class WebDAV(TableBase, table=True):
-    __tablename__ = 'webdavs'
+    """WebDAV账户模型"""
+
     __table_args__ = (UniqueConstraint("name", "user_id", name="uq_webdav_name_user"),)
 
     name: str = Field(max_length=255, description="WebDAV账户名")
-    password: str = Field(max_length=255, description="WebDAV密码（加密后）")
+    password: str = Field(max_length=255, description="WebDAV密码")
     root: str = Field(default="/", sa_column_kwargs={"server_default": "'/'"}, description="根目录路径")
     readonly: bool = Field(default=False, sa_column_kwargs={"server_default": text("false")}, description="是否只读")
     use_proxy: bool = Field(default=False, sa_column_kwargs={"server_default": text("false")}, description="是否使用代理下载")
     
     # 外键
-    user_id: int = Field(foreign_key="users.id", index=True, description="所属用户ID")
+    user_id: int = Field(foreign_key="user.id", index=True, description="所属用户ID")
     
     # 关系
     user: "User" = Relationship(back_populates="webdavs")