refactor: standardize dialog components to use consistent DialogFooter styling

Remove custom styling from DialogFooter components across the application
to ensure consistent appearance and behavior. All dialogs now follow the
unified layout pattern defined in the base Dialog component.

Changes:
- Remove custom className overrides from DialogFooter in:
  - EndpointSpeedTest.tsx
  - CodexQuickWizardModal.tsx
  - CodexCommonConfigModal.tsx
  - ClaudeConfigEditor.tsx
- Fix McpWizardModal content area padding (remove -mx-6 negative margin)
- Fix McpPanel to use DialogFooter component instead of custom div

All dialogs now consistently use:
- DialogHeader: px-6 pt-6 pb-4 with border and background (built-in)
- Content area: flex-1 overflow-y-auto px-6 py-4
- DialogFooter: px-6 pb-6 pt-4 with border and background (built-in)

This ensures proper spacing, alignment, and visual consistency across
all modal dialogs in the application.

src/components/mcp/McpWizardModal.tsx

@@ -228,7 +228,7 @@ const McpWizardModal: React.FC<McpWizardModalProps> = ({
         </DialogHeader>
 
         {/* Content */}
-        <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">
           {/* Hint */}
           <div className="rounded-lg border border-blue-200 bg-blue-50 p-3 dark:border-blue-800 dark:bg-blue-900/20">
             <p className="text-sm text-blue-800 dark:text-blue-200">