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

.env.example

@@ -3,7 +3,10 @@ NEXT_PUBLIC_SHOPIFY_DOMAIN=mock.shop
 # NEXT_PUBLIC_SHOPIFY_STOREFRONT_ACCESS_TOKEN=
 # NEXT_PUBLIC_SHOPIFY_API_VERSION=2025-07
 
+# Store assistant — set to 1 to show the Ask launcher; anything else hides it
+NEXT_PUBLIC_ENABLE_AI=0
+
 # Store assistant (/api/chat) — https://openrouter.ai/keys
 OPENROUTER_API_KEY=
-# Optional; defaults to anthropic/claude-sonnet-4.5
+# Optional; defaults to openai/gpt-5.6-luna-pro
 # OPENROUTER_MODEL=