✨ feat(font): 新增系统字体枚举与全局字体配置能力

- 新增 Go 侧已安装字体扫描接口，支持前端读取系统真实字体列表
- 接入 Wails 字体查询导出，补齐 App.d.ts 与 App.js 调用声明
- 新增字体选项构建与匹配工具，区分 UI 字体与等宽字体候选
- 外观设置支持按平台加载字体列表，并支持搜索匹配与默认字体回退
- Store 增加自定义 UI 字体与代码字体配置，持久化全局字体选择

frontend/src/store.test.ts

@@ -75,6 +75,8 @@ describe('store appearance persistence', () => {
     expect(appearance.dataTableFontSizeFollowGlobal).toBe(true);
     expect(appearance.sidebarTreeFontSize).toBeNull();
     expect(appearance.sidebarTreeFontSizeFollowGlobal).toBe(true);
+    expect(appearance.customUIFontFamily).toBeNull();
+    expect(appearance.customMonoFontFamily).toBeNull();
   });
 
   it('persists DataGrid appearance settings and restores them after reload', async () => {
@@ -97,6 +99,26 @@ describe('store appearance persistence', () => {
     expect(appearance.dataTableDensity).toBe('compact');
   });
 
+  it('persists custom font families and sanitizes blank values', async () => {
+    const { useStore } = await importStore();
+
+    useStore.getState().setAppearance({
+      customUIFontFamily: '  IBM Plex Sans, PingFang SC  ',
+      customMonoFontFamily: '   ',
+    });
+
+    let appearance = useStore.getState().appearance;
+    expect(appearance.customUIFontFamily).toBe('IBM Plex Sans, PingFang SC');
+    expect(appearance.customMonoFontFamily).toBeNull();
+
+    vi.resetModules();
+    const reloaded = await importStore();
+    appearance = reloaded.useStore.getState().appearance;
+
+    expect(appearance.customUIFontFamily).toBe('IBM Plex Sans, PingFang SC');
+    expect(appearance.customMonoFontFamily).toBeNull();
+  });
+
   it('does not clear persisted legacy connections during hydration migration', async () => {
     storage.setItem('lite-db-storage', JSON.stringify({
       state: {