refactor(theme): drop unused MouseEvent param from setTheme

Now that the view transition animation is gone, setTheme no longer
needs click coordinates. Reduce the API surface to (theme: Theme) =>
void and simplify the call sites in mode-toggle and ThemeSettings.

src/components/mode-toggle.tsx

@@ -7,13 +7,11 @@ export function ModeToggle() {
   const { theme, setTheme } = useTheme();
   const { t } = useTranslation();
 
-  const toggleTheme = (event: React.MouseEvent) => {
-    // 如果当前是 dark 或 system（且系统是暗色），切换到 light
-    // 否则切换到 dark
+  const toggleTheme = () => {
     if (theme === "dark") {
-      setTheme("light", event);
+      setTheme("light");
     } else {
-      setTheme("dark", event);
+      setTheme("dark");
     }
   };