feat(frontend): Transform layout to use shadcn dashboard-01 with iOS PWA safe area support.

- Replace custom layout with modern SidebarProvider/SidebarInset structure
- Add AppSidebar component using shadcn patterns with preserved account summary
- Add SiteHeader component with SidebarTrigger integration
- Install shadcn sidebar, separator, and related UI components
- Fix iOS PWA safe area issues - sidebar no longer overlaps dynamic island/notch
- Add pt-safe-top and pl-safe-left classes to sidebar and header components
- Remove legacy Sidebar.tsx and Header.tsx components
- Preserve all existing functionality: navigation, API health status, theme toggle, PWA features
- Improve mobile responsive behavior with built-in shadcn drawer patterns

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/components/ui/button.tsx

@@ -1,8 +1,8 @@
-import * as React from "react";
-import { Slot } from "@radix-ui/react-slot";
-import { cva, type VariantProps } from "class-variance-authority";
+import * as React from "react"
+import { Slot } from "@radix-ui/react-slot"
+import { cva, type VariantProps } from "class-variance-authority"
 
-import { cn } from "@/lib/utils";
+import { cn } from "@/lib/utils"
 
 const buttonVariants = cva(
   "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0",
@@ -31,27 +31,27 @@ const buttonVariants = cva(
       variant: "default",
       size: "default",
     },
-  },
-);
+  }
+)
 
 export interface ButtonProps
   extends React.ButtonHTMLAttributes<HTMLButtonElement>,
     VariantProps<typeof buttonVariants> {
-  asChild?: boolean;
+  asChild?: boolean
 }
 
 const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
   ({ className, variant, size, asChild = false, ...props }, ref) => {
-    const Comp = asChild ? Slot : "button";
+    const Comp = asChild ? Slot : "button"
     return (
       <Comp
         className={cn(buttonVariants({ variant, size, className }))}
         ref={ref}
         {...props}
       />
-    );
-  },
-);
-Button.displayName = "Button";
+    )
+  }
+)
+Button.displayName = "Button"
 
-export { Button, buttonVariants };
+export { Button, buttonVariants }