Support custom WebUI fonts and UI additions

Backend: add CheckWebUIFontExist API and route; set --font-family-mono CSS variable in InitWebUi for aacute/custom/default. Improve webui font uploader: force saved filename to CustomFont, robustly clean old webui/CustomFont files, and log failures.

Frontend: add FileManager.checkWebUIFontExists; update theme settings to show upload UI only when 'custom' is selected, display uploaded status, attempt delete-before-upload, reload after actions, and adjust Accordion props. ColorPicker: enable pointer events on PopoverContent to allow dragging. applyFont now sets --font-family-mono for all modes.

packages/napcat-webui-frontend/src/components/ColorPicker.tsx

@@ -5,8 +5,8 @@ import { ColorResult, SketchPicker } from 'react-color';
 // 假定 heroui 提供的 Popover组件
 
 interface ColorPickerProps {
-  color: string
-  onChange: (color: ColorResult) => void
+  color: string;
+  onChange: (color: ColorResult) => void;
 }
 
 const ColorPicker: React.FC<ColorPickerProps> = ({ color, onChange }) => {
@@ -22,7 +22,8 @@ const ColorPicker: React.FC<ColorPickerProps> = ({ color, onChange }) => {
           style={{ background: color }}
         />
       </PopoverTrigger>
-      <PopoverContent>
+      {/* 移除 PopoverContent 默认的事件阻止，允许鼠标拖动到外部 */}
+      <PopoverContent className='pointer-events-auto'>
         <SketchPicker
           color={color}
           onChange={handleChange}