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/redeem.py

@@ -1,14 +1,11 @@
-
-from typing import Optional
-from sqlmodel import Field, text, Column, func, DateTime
+from sqlmodel import Field, text
 from .base import TableBase
-from datetime import datetime
 
 class Redeem(TableBase, table=True):
-    __tablename__ = 'redeems'
+    """兑换码模型"""
 
     type: int = Field(description="兑换码类型")
-    product_id: Optional[int] = Field(default=None, description="关联的商品/权益ID")
+    product_id: int | None = Field(default=None, description="关联的商品/权益ID")
     num: int = Field(default=1, sa_column_kwargs={"server_default": "1"}, description="可兑换数量/时长等")
     code: str = Field(unique=True, index=True, description="兑换码，唯一")
     used: bool = Field(default=False, sa_column_kwargs={"server_default": text("false")}, description="是否已使用")