Add HTTP exception helpers and update models

Introduced utils/http/http_exceptions.py with common HTTP exception helpers for FastAPI. Updated main.py to use a global exception handler that logs and hides internal errors. Refined models/README.md to document new models and relationships, including PhysicalFile and UploadSession, and updated DTO and enum documentation. Simplified ThemeResponse in models/color.py. Improved models/download.py with type annotations, index changes, and import optimizations. Fixed a parameter type in clean.py.

Co-Authored-By: 砂糖橘 <54745033+Foxerine@users.noreply.github.com>

models/color.py

@@ -3,29 +3,5 @@ from .base import SQLModelBase
 class ThemeResponse(SQLModelBase):
     """主题响应 DTO"""
 
-    primary: str = "#3f51b5"
-    """主色调"""
-
-    secondary: str = "#f50057"
-    """次要色"""
-
-    accent: str = "#9c27b0"
-    """强调色"""
-
-    dark: str = "#1d1d1d"
-    """深色"""
-
-    dark_page: str = "#121212"
-    """深色页面背景"""
-
-    positive: str = "#21ba45"
-    """正面/成功色"""
-
-    negative: str = "#c10015"
-    """负面/错误色"""
-
-    info: str = "#31ccec"
-    """信息色"""
-
-    warning: str = "#f2c037"
-    """警告色"""
+    pass
+