feat(web): add chat UI with WebSocket streaming and conversation persistence

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/client/src/components/chat/ChatMessage.tsx

@@ -0,0 +1,19 @@
+import { cn } from '@/lib/utils';
+import type { Message } from '@/types';
+
+export function ChatMessage({ message }: { message: Message }) {
+  const isUser = message.role === 'user';
+
+  return (
+    <div className={cn('mb-4 flex', isUser ? 'justify-end' : 'justify-start')}>
+      <div
+        className={cn(
+          'max-w-[80%] rounded-lg px-4 py-2.5 text-sm leading-relaxed',
+          isUser ? 'bg-zinc-800 text-zinc-100' : 'bg-zinc-900 text-zinc-300 border border-zinc-800'
+        )}
+      >
+        {message.content}
+      </div>
+    </div>
+  );
+}