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/storage_pack.py

@@ -9,15 +9,15 @@ if TYPE_CHECKING:
     from .user import User
 
 class StoragePack(TableBase, table=True):
-    __tablename__ = 'storage_packs'
+    """容量包模型"""
 
     name: str = Field(max_length=255, description="容量包名称")
-    active_time: Optional[datetime] = Field(default=None, description="激活时间")
-    expired_time: Optional[datetime] = Field(default=None, index=True, description="过期时间")
+    active_time: datetime | None = Field(default=None, description="激活时间")
+    expired_time: datetime | None = Field(default=None, index=True, description="过期时间")
     size: int = Field(description="容量包大小（字节）")
     
     # 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="storage_packs")