feat(chat): enhance chat interface with markdown support

- Add markdown rendering with react-markdown and remark-gfm
- Create ChatMessage component with code copy functionality
- Add typing indicator animation during AI response
- Create welcome screen for new users
- Add Textarea component for multi-line input
- Improve message styling with avatars and hover actions
- Add Gateway connection status awareness
- Add prose styling for markdown content

src/components/ui/textarea.tsx

@@ -0,0 +1,22 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+const Textarea = React.forwardRef<
+  HTMLTextAreaElement,
+  React.ComponentProps<"textarea">
+>(({ className, ...props }, ref) => {
+  return (
+    <textarea
+      className={cn(
+        "flex min-h-[80px] w-full rounded-md border border-input bg-background px-3 py-2 text-base ring-offset-background placeholder:text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:cursor-not-allowed disabled:opacity-50 md:text-sm",
+        className
+      )}
+      ref={ref}
+      {...props}
+    />
+  )
+})
+Textarea.displayName = "Textarea"
+
+export { Textarea }