refactor: migrate all MCP dialogs to shadcn/ui Dialog component

Convert all MCP-related modal windows to use the unified shadcn/ui Dialog
component for consistency with the rest of the application.

Changes:
- McpPanel: Replace custom modal with Dialog component
  - Update props from onClose to open/onOpenChange pattern
  - Use DialogContent, DialogHeader, DialogTitle components
  - Remove custom backdrop and close button (handled by Dialog)

- McpFormModal: Migrate form modal to Dialog
  - Wrap entire form in Dialog component structure
  - Use DialogFooter for action buttons
  - Apply variant="mcp" to maintain green button styling
  - Remove unused X icon import

- McpWizardModal: Convert wizard to Dialog
  - Replace custom modal structure with Dialog components
  - Use Button component with variant="mcp" for consistency
  - Remove unused isLinux and X icon imports

- App.tsx: Update McpPanel usage
  - Remove conditional rendering wrapper
  - Pass open and onOpenChange props directly

- dialog.tsx: Fix dialog overlay and content styling
  - Change overlay from bg-background/80 to bg-black/50 for consistency
  - Change content from bg-background to explicit bg-white dark:bg-gray-900
  - Ensures opaque backgrounds matching MCP panel style

Benefits:
- Unified dialog behavior across the application
- Consistent styling and animations
- Better accessibility with Radix UI primitives
- Reduced code duplication
- Maintains MCP-specific green color scheme

All dialogs now share the same base styling while preserving their unique
content and functionality.

src/components/ui/dialog.tsx

@@ -18,7 +18,7 @@ const DialogOverlay = React.forwardRef<
   <DialogPrimitive.Overlay
     ref={ref}
     className={cn(
-      "fixed inset-0 z-50 bg-background/80 backdrop-blur-sm data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0",
+      "fixed inset-0 z-50 bg-black/50 backdrop-blur-sm data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0",
       className,
     )}
     {...props}
@@ -35,7 +35,7 @@ const DialogContent = React.forwardRef<
     <DialogPrimitive.Content
       ref={ref}
       className={cn(
-        "fixed left-1/2 top-1/2 z-50 grid w-full max-w-lg translate-x-[-50%] translate-y-[-50%] gap-4 border bg-background p-6 shadow-lg duration-200 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[state=closed]:slide-out-to-left-1/2 data-[state=closed]:slide-out-to-top-[48%] data-[state=open]:slide-in-from-left-1/2 data-[state=open]:slide-in-from-top-[48%] sm:rounded-lg",
+        "fixed left-1/2 top-1/2 z-50 grid w-full max-w-lg translate-x-[-50%] translate-y-[-50%] gap-4 border bg-white dark:bg-gray-900 p-6 shadow-lg duration-200 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[state=closed]:slide-out-to-left-1/2 data-[state=closed]:slide-out-to-top-[48%] data-[state=open]:slide-in-from-left-1/2 data-[state=open]:slide-in-from-top-[48%] sm:rounded-lg",
         className,
       )}
       {...props}