feat: 合并 File 和 Folder 模型为统一的 Object 模型，优化对象管理逻辑

refactor: 更新相关模型和路由以支持新对象模型，移除冗余代码

models/share.py

@@ -1,42 +1,71 @@
 
-from typing import Optional, TYPE_CHECKING
+from typing import TYPE_CHECKING
 from datetime import datetime
-from sqlmodel import Field, Relationship, text, CheckConstraint, UniqueConstraint, Index
+from sqlmodel import Field, Relationship, text, UniqueConstraint, Index
 from .base import TableBase
-from datetime import datetime
 
 if TYPE_CHECKING:
     from .user import User
     from .report import Report
+    from .object import Object
+
 
 class Share(TableBase, table=True):
     """分享模型"""
 
     __table_args__ = (
         UniqueConstraint("code", name="uq_share_code"),
-        CheckConstraint("(file_id IS NOT NULL) <> (folder_id IS NOT NULL)", name="ck_share_xor"),
         Index("ix_share_source_name", "source_name"),
         Index("ix_share_user_created", "user_id", "created_at"),
+        Index("ix_share_object", "object_id"),
     )
 
-    code: str = Field(max_length=64, nullable=False, index=True, description="分享码")
-    password: str | None = Field(default=None, max_length=255, description="分享密码（加密后）")
-    
-    is_dir: bool = Field(default=False, sa_column_kwargs={"server_default": text("false")}, description="是否为目录分享")
-    file_id: int | None = Field(default=None, foreign_key="file.id", index=True, description="文件ID（二选一）")
-    folder_id: int | None = Field(default=None, foreign_key="folder.id", index=True, description="目录ID（二选一）")
-    
-    views: int = Field(default=0, sa_column_kwargs={"server_default": "0"}, description="浏览次数")
-    downloads: int = Field(default=0, sa_column_kwargs={"server_default": "0"}, description="下载次数")
-    remain_downloads: int | None = Field(default=None, description="剩余下载次数 (NULL为不限制)")
-    expires: datetime | None = Field(default=None, description="过期时间 (NULL为永不过期)")
-    preview_enabled: bool = Field(default=True, sa_column_kwargs={"server_default": text("true")}, description="是否允许预览")
-    source_name: str | None = Field(default=None, max_length=255, description="源名称（冗余字段，便于展示）")
-    score: int = Field(default=0, sa_column_kwargs={"server_default": "0"}, description="兑换此分享所需的积分")
-    
+    code: str = Field(max_length=64, nullable=False, index=True)
+    """分享码"""
+
+    password: str | None = Field(default=None, max_length=255)
+    """分享密码（加密后）"""
+
+    object_id: int = Field(foreign_key="object.id", index=True)
+    """关联的对象ID"""
+
+    views: int = Field(default=0, sa_column_kwargs={"server_default": "0"})
+    """浏览次数"""
+
+    downloads: int = Field(default=0, sa_column_kwargs={"server_default": "0"})
+    """下载次数"""
+
+    remain_downloads: int | None = None
+    """剩余下载次数 (NULL为不限制)"""
+
+    expires: datetime | None = None
+    """过期时间 (NULL为永不过期)"""
+
+    preview_enabled: bool = Field(default=True, sa_column_kwargs={"server_default": text("true")})
+    """是否允许预览"""
+
+    source_name: str | None = Field(default=None, max_length=255)
+    """源名称（冗余字段，便于展示）"""
+
+    score: int = Field(default=0, sa_column_kwargs={"server_default": "0"})
+    """兑换此分享所需的积分"""
+
     # 外键
-    user_id: int = Field(foreign_key="user.id", index=True, description="创建分享的用户ID")
-    
+    user_id: int = Field(foreign_key="user.id", index=True)
+    """创建分享的用户ID"""
+
     # 关系
     user: "User" = Relationship(back_populates="shares")
-    reports: list["Report"] = Relationship(back_populates="share")
+    """分享创建者"""
+
+    object: "Object" = Relationship(back_populates="shares")
+    """关联的对象"""
+
+    reports: list["Report"] = Relationship(back_populates="share")
+    """举报列表"""
+
+    @property
+    def is_dir(self) -> bool:
+        """是否为目录分享（向后兼容属性）"""
+        from .object import ObjectType
+        return self.object.type == ObjectType.FOLDER if self.object else False