fix: unify dialog layout and fix content padding issues

- Fix negative margin overflow in all dialog content areas
- Standardize dialog structure with flex-col layout
- Add consistent py-4 spacing to all content areas
- Ensure proper spacing between header, content, and footer

Affected components:
- AddProviderDialog, EditProviderDialog
- McpFormModal, McpPanel
- UsageScriptModal
- SettingsDialog

All dialogs now follow unified layout pattern:
- DialogContent: flex flex-col max-h-[90vh]
- Content area: flex-1 overflow-y-auto px-6 py-4
- No negative margins that cause content overflow

src/components/settings/ThemeSettings.tsx

@@ -52,7 +52,12 @@ interface ThemeButtonProps {
   children: React.ReactNode;
 }
 
-function ThemeButton({ active, onClick, icon: Icon, children }: ThemeButtonProps) {
+function ThemeButton({
+  active,
+  onClick,
+  icon: Icon,
+  children,
+}: ThemeButtonProps) {
   return (
     <Button
       type="button"