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/hover-card.tsx

@@ -0,0 +1,44 @@
+"use client"
+
+import * as React from "react"
+import { HoverCard as HoverCardPrimitive } from "radix-ui"
+
+import { cn } from "@/lib/utils"
+
+function HoverCard({
+  ...props
+}: React.ComponentProps<typeof HoverCardPrimitive.Root>) {
+  return <HoverCardPrimitive.Root data-slot="hover-card" {...props} />
+}
+
+function HoverCardTrigger({
+  ...props
+}: React.ComponentProps<typeof HoverCardPrimitive.Trigger>) {
+  return (
+    <HoverCardPrimitive.Trigger data-slot="hover-card-trigger" {...props} />
+  )
+}
+
+function HoverCardContent({
+  className,
+  align = "center",
+  sideOffset = 4,
+  ...props
+}: React.ComponentProps<typeof HoverCardPrimitive.Content>) {
+  return (
+    <HoverCardPrimitive.Portal data-slot="hover-card-portal">
+      <HoverCardPrimitive.Content
+        data-slot="hover-card-content"
+        align={align}
+        sideOffset={sideOffset}
+        className={cn(
+          "z-50 w-64 origin-(--radix-hover-card-content-transform-origin) rounded-md border bg-popover p-4 text-popover-foreground shadow-md outline-hidden data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95 data-[state=open]:animate-in data-[state=open]:fade-in-0 data-[state=open]:zoom-in-95",
+          className
+        )}
+        {...props}
+      />
+    </HoverCardPrimitive.Portal>
+  )
+}
+
+export { HoverCard, HoverCardTrigger, HoverCardContent }