Add AI store assistant with catalogue tool calls

- /api/chat streams via AI SDK v7 through OpenRouter (OPENROUTER_API_KEY),
  with a store-specific system prompt and five read-only tools:
  searchCatalogue, getProductDetails, listCollections,
  getCollectionProducts, browseProducts
- Sidebar assistant on the right that opens from a launcher and expands,
  built on ai-elements (conversation, message, prompt-input, tool) with
  shimmer on in-flight tool calls
- Extract services/shopify/catalog.ts so the Storefront fetchers have no
  React imports and can run in a Route Handler; the client hooks now
  re-export from it
- ai-elements pulled in the canonical shadcn primitives, replacing the
  hand-rolled command/dialog/button variants; search dialog moved to the
  cmdk-based Command and CommandDialog forwards shouldFilter
- Pin shiki to ^3.19.0 to match streamdown and drop the duplicate copy
- Add .env.example documenting the required env vars

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

components/ui/spinner.tsx

@@ -1,38 +1,16 @@
-import React from 'react';
-import { cn } from '@/lib/utils';
+import { Loader2Icon } from "lucide-react"
 
-interface SpinnerProps extends React.ComponentProps<'svg'> {
-  size?: 'sm' | 'md' | 'lg' | 'xl';
-}
+import { cn } from "@/lib/utils"
 
-const sizeClasses = {
-  sm: 'size-3',
-  md: 'size-4',
-  lg: 'size-6',
-  xl: 'size-8',
-};
-
-function Spinner({ className, size = 'md', ...props }: SpinnerProps) {
+function Spinner({ className, ...props }: React.ComponentProps<"svg">) {
   return (
-    <svg
+    <Loader2Icon
       role="status"
       aria-label="Loading"
-      xmlns="http://www.w3.org/2000/svg"
-      width="24"
-      height="24"
-      viewBox="0 0 24 24"
-      fill="none"
-      stroke="currentColor"
-      strokeWidth="2"
-      strokeLinecap="round"
-      strokeLinejoin="round"
-      className={cn('animate-spin', sizeClasses[size], className)}
+      className={cn("size-4 animate-spin", className)}
       {...props}
-    >
-      <path d="M21 12a9 9 0 1 1-6.219-8.56" />
-    </svg>
-  );
+    />
+  )
 }
 
-export { Spinner };
-export type { SpinnerProps };
+export { Spinner }