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/UsageScriptModal.tsx

@@ -179,7 +179,7 @@ const UsageScriptModal: React.FC<UsageScriptModalProps> = ({
         </DialogHeader>
 
         {/* Content - Scrollable */}
-        <div className="flex-1 overflow-y-auto -mx-6 px-6 space-y-4">
+        <div className="flex-1 overflow-y-auto px-6 py-4 space-y-4">
           {/* 启用开关 */}
           <label className="flex items-center gap-2 cursor-pointer">
             <input