feat(07-01): add useWizardState hook, i18n keys, and shadcn checkbox

- Create useWizardState hook with localStorage persistence keyed by userId
- Add all setup wizard i18n keys to en.json and de.json
- Install shadcn checkbox component for step 2 item selection

src/components/ui/checkbox.tsx

@@ -0,0 +1,30 @@
+import * as React from "react"
+import { CheckIcon } from "lucide-react"
+import { Checkbox as CheckboxPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function Checkbox({
+  className,
+  ...props
+}: React.ComponentProps<typeof CheckboxPrimitive.Root>) {
+  return (
+    <CheckboxPrimitive.Root
+      data-slot="checkbox"
+      className={cn(
+        "peer size-4 shrink-0 rounded-[4px] border border-input shadow-xs transition-shadow outline-none focus-visible:border-ring focus-visible:ring-[3px] focus-visible:ring-ring/50 disabled:cursor-not-allowed disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-destructive/20 data-[state=checked]:border-primary data-[state=checked]:bg-primary data-[state=checked]:text-primary-foreground dark:bg-input/30 dark:aria-invalid:ring-destructive/40 dark:data-[state=checked]:bg-primary",
+        className
+      )}
+      {...props}
+    >
+      <CheckboxPrimitive.Indicator
+        data-slot="checkbox-indicator"
+        className="grid place-content-center text-current transition-none"
+      >
+        <CheckIcon className="size-3.5" />
+      </CheckboxPrimitive.Indicator>
+    </CheckboxPrimitive.Root>
+  )
+}
+
+export { Checkbox }