refactor: 统一 sqlmodel_ext 用法至官方推荐模式

- 替换 Field(max_length=X) 为 StrX/TextX 类型别名（21 个 sqlmodels 文件）
- 替换 get + 404 检查为 get_exist_one()（17 个路由文件，约 50 处）
- 替换 save + session.refresh 为 save(load=...)
- 替换 session.add + commit 为 save()（dav/provider.py）
- 更新所有依赖至最新版本

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sqlmodels/storage_pack.py

@@ -1,23 +1,60 @@
-
-from typing import TYPE_CHECKING
 from datetime import datetime
+from typing import TYPE_CHECKING
 from uuid import UUID
 
-from sqlmodel import Field, Relationship, Column, func, DateTime
+from sqlalchemy import BigInteger
+from sqlmodel import Field, Relationship
 
-from sqlmodel_ext import SQLModelBase, TableBaseMixin
+from sqlmodel_ext import SQLModelBase, TableBaseMixin, Str255
 
 if TYPE_CHECKING:
     from .user import User
 
+
+# ==================== DTO 模型 ====================
+
+class StoragePackResponse(SQLModelBase):
+    """容量包响应 DTO"""
+
+    id: int
+    """容量包ID"""
+
+    name: str
+    """容量包名称"""
+
+    size: int
+    """容量大小（字节）"""
+
+    active_time: datetime | None = None
+    """激活时间"""
+
+    expired_time: datetime | None = None
+    """过期时间"""
+
+    product_id: UUID | None = None
+    """来源商品UUID"""
+
+
+# ==================== 数据库模型 ====================
+
 class StoragePack(SQLModelBase, TableBaseMixin):
     """容量包模型"""
 
-    name: str = Field(max_length=255, description="容量包名称")
-    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）")
-    
+    name: Str255
+    """容量包名称"""
+
+    active_time: datetime | None = None
+    """激活时间"""
+
+    expired_time: datetime | None = Field(default=None, index=True)
+    """过期时间"""
+
+    size: int = Field(sa_type=BigInteger)
+    """容量包大小（字节）"""
+
+    product_id: UUID | None = Field(default=None, foreign_key="product.id", ondelete="SET NULL")
+    """来源商品UUID"""
+
     # 外键
     user_id: UUID = Field(
         foreign_key="user.id",
@@ -25,6 +62,17 @@ class StoragePack(SQLModelBase, TableBaseMixin):
         ondelete="CASCADE"
     )
     """所属用户UUID"""
-    
+
     # 关系
-    user: "User" = Relationship(back_populates="storage_packs")
+    user: "User" = Relationship(back_populates="storage_packs")
+
+    def to_response(self) -> StoragePackResponse:
+        """转换为响应 DTO"""
+        return StoragePackResponse(
+            id=self.id,
+            name=self.name,
+            size=self.size,
+            active_time=self.active_time,
+            expired_time=self.expired_time,
+            product_id=self.product_id,
+        )