Refine the store assistant UI and gate it behind a flag

- Gate the assistant on NEXT_PUBLIC_ENABLE_AI=1 (UI only; the /api/chat
  route still responds if called directly)
- Chat model is openai/gpt-5.6-luna-pro with reasoning requested and
  sendReasoning enabled, rendered via the Reasoning component
- Suggestion chips and reasoning come from ai-elements; attachments gain
  hover-card previews, left alignment, and render under the user message
- Launcher: plain Button when closed, magicui RainbowButton when open
- Tool results replace the collapsible Tool UI with a shimmer while
  running and a muted icon + summary line after, plus product previews
- Commerce icons in place of the folder icon for collections
- Add a thin announcement bar above the header; footer splits links and
  socials onto separate rows and clears the launcher corner
- Add the shadcn base layer so Tailwind v4's bare `border` picks up the
  theme colour instead of currentColor

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jWbNNJLksC1QG8z8845FX

components/ui/scroll-area.tsx

@@ -0,0 +1,58 @@
+"use client"
+
+import * as React from "react"
+import { ScrollArea as ScrollAreaPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function ScrollArea({
+  className,
+  children,
+  ...props
+}: React.ComponentProps<typeof ScrollAreaPrimitive.Root>) {
+  return (
+    <ScrollAreaPrimitive.Root
+      data-slot="scroll-area"
+      className={cn("relative", className)}
+      {...props}
+    >
+      <ScrollAreaPrimitive.Viewport
+        data-slot="scroll-area-viewport"
+        className="size-full rounded-[inherit] transition-[color,box-shadow] outline-none focus-visible:ring-[3px] focus-visible:ring-ring/50 focus-visible:outline-1"
+      >
+        {children}
+      </ScrollAreaPrimitive.Viewport>
+      <ScrollBar />
+      <ScrollAreaPrimitive.Corner />
+    </ScrollAreaPrimitive.Root>
+  )
+}
+
+function ScrollBar({
+  className,
+  orientation = "vertical",
+  ...props
+}: React.ComponentProps<typeof ScrollAreaPrimitive.ScrollAreaScrollbar>) {
+  return (
+    <ScrollAreaPrimitive.ScrollAreaScrollbar
+      data-slot="scroll-area-scrollbar"
+      orientation={orientation}
+      className={cn(
+        "flex touch-none p-px transition-colors select-none",
+        orientation === "vertical" &&
+          "h-full w-2.5 border-l border-l-transparent",
+        orientation === "horizontal" &&
+          "h-2.5 flex-col border-t border-t-transparent",
+        className
+      )}
+      {...props}
+    >
+      <ScrollAreaPrimitive.ScrollAreaThumb
+        data-slot="scroll-area-thumb"
+        className="relative flex-1 rounded-full bg-border"
+      />
+    </ScrollAreaPrimitive.ScrollAreaScrollbar>
+  )
+}
+
+export { ScrollArea, ScrollBar }