feat: 重构主题相关逻辑，移动 ThemeResponse 到 color.py，更新相关引用，优化目录路径处理

models/color.py

@@ -0,0 +1,31 @@
+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"""