feat: Implement API routers for user, tag, vas, webdav, and slave functionalities

- Added user authentication and registration endpoints with JWT support.
- Created tag management routes for creating and deleting tags.
- Implemented value-added service (VAS) endpoints for managing storage packs and orders.
- Developed WebDAV account management routes for creating, updating, and deleting accounts.
- Introduced slave router for handling file uploads, downloads, and aria2 task management.
- Enhanced JWT utility functions for token creation and secret key management.
- Established lifespan management for FastAPI application startup and shutdown processes.
- Integrated password handling utilities with Argon2 hashing and two-factor authentication support.

models/group.py

@@ -8,6 +8,7 @@ from .base import TableBase, SQLModelBase, UUIDTableBase
 
 if TYPE_CHECKING:
     from .user import User
+    from .policy import Policy
 
 
 # ==================== Base 模型 ====================
@@ -70,6 +71,10 @@ class GroupResponse(GroupBase, GroupOptionsBase):
 
 # ==================== 数据库模型 ====================
 
+# GroupPolicyLink 定义在 policy.py 中以避免循环导入
+from .policy import GroupPolicyLink
+
+
 class GroupOptions(GroupOptionsBase, TableBase, table=True):
     """用户组选项模型"""
 
@@ -104,9 +109,6 @@ class Group(GroupBase, UUIDTableBase, table=True):
     name: str = Field(max_length=255, unique=True)
     """用户组名"""
 
-    policies: str | None = Field(default=None, max_length=255)
-    """允许的策略ID列表，逗号分隔"""
-
     max_storage: int = Field(default=0, sa_column_kwargs={"server_default": "0"})
     """最大存储空间（字节）"""
 
@@ -128,6 +130,12 @@ class Group(GroupBase, UUIDTableBase, table=True):
         sa_relationship_kwargs={"uselist": False}
     )
 
+    # 多对多关系：用户组可以关联多个存储策略
+    policies: list["Policy"] = Relationship(
+        back_populates="groups",
+        link_model=GroupPolicyLink,
+    )
+
     # 关系：一个组可以有多个用户
     user: list["User"] = Relationship(
         back_populates="group",