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/order.py

@@ -1,26 +1,25 @@
 
-from typing import Optional, TYPE_CHECKING
-from sqlmodel import Field, Relationship, Column, func, DateTime
+from typing import TYPE_CHECKING
+from sqlmodel import Field, Relationship
 from .base import TableBase
-from datetime import datetime
 
 if TYPE_CHECKING:
     from .user import User
 
 class Order(TableBase, table=True):
-    __tablename__ = 'orders'
+    """订单模型"""
 
     order_no: str = Field(max_length=255, unique=True, index=True, description="订单号，唯一")
     type: int = Field(description="订单类型")
-    method: Optional[str] = Field(default=None, max_length=255, description="支付方式")
-    product_id: Optional[int] = Field(default=None, description="商品ID")
+    method: str | None = Field(default=None, max_length=255, description="支付方式")
+    product_id: int | None = Field(default=None, description="商品ID")
     num: int = Field(default=1, sa_column_kwargs={"server_default": "1"}, description="购买数量")
     name: str = Field(max_length=255, description="商品名称")
     price: int = Field(default=0, sa_column_kwargs={"server_default": "0"}, description="订单价格（分）")
     status: int = Field(default=0, sa_column_kwargs={"server_default": "0"}, description="订单状态: 0=待支付, 1=已完成, 2=已取消")
     
     # 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="orders")