fix: store session token on signup and send it to /chat

- web: App stores sessionToken and passes to useChat; useChat sends Authorization header
- web: ChatPanel adds wursor-message-user/agent test hooks
- verified full UI flow (signup -> chat -> working -> reply -> approve -> preview)

web/src/App.tsx

@@ -5,15 +5,29 @@ import { Preview } from './components/Preview.tsx';
 import { SignUp } from './components/SignUp.tsx';
 import { useChat } from './hooks/useChat.ts';
 
-export function App() {
-  const [signedUp, setSignedUp] = useState(false);
-  const [applied, setApplied] = useState(false);
-  const chat = useChat();
+async function signUp(email: string, password: string): Promise<string> {
+  const res = await fetch('/auth/signup', {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ email, password }),
+  });
+  if (!res.ok) {
+    const body = (await res.json().catch(() => null)) as { error?: string } | null;
+    throw new Error(body?.error ?? 'Sign up failed');
+  }
+  const body = (await res.json()) as { sessionToken: string };
+  return body.sessionToken;
+}
 
-  if (!signedUp) {
+export function App() {
+  const [sessionToken, setSessionToken] = useState<string | null>(null);
+  const [applied, setApplied] = useState(false);
+  const chat = useChat(sessionToken);
+
+  if (sessionToken === null) {
     return (
       <div className="auth-screen">
-        <SignUp onSignUp={async () => setSignedUp(true)} />
+        <SignUp onSignUp={async (email, password) => setSessionToken(await signUp(email, password))} />
       </div>
     );
   }

web/src/components/ChatPanel.tsx

@@ -30,7 +30,7 @@ export function ChatPanel({ messages, status, onSend }: ChatPanelProps) {
         ) : (
           <ul className="chat-list">
             {messages.map((message) => (
-              <li key={message.id} className={`message message-${message.role}`}>
+              <li key={message.id} className={`message message-${message.role} wursor-message-${message.role}`}>
                 {message.text}
               </li>
             ))}

web/src/hooks/useChat.ts

@@ -14,12 +14,13 @@ function mockReply(text: string, heading: string | undefined): string {
     : 'Done — your change is ready to preview.';
 }
 
-export function useChat() {
+export function useChat(sessionToken: string | null) {
   const [messages, setMessages] = useState<ChatMessage[]>([]);
   const [status, setStatus] = useState<ChatStatus>('idle');
   const [heading, setHeading] = useState('Welcome to our site');
 
-  const send = useCallback(async (text: string) => {
+  const send = useCallback(
+    async (text: string) => {
       const nextHeading = extractHeading(text);
       setMessages((prev) => [...prev, { id: crypto.randomUUID(), role: 'user', text }]);
       setStatus('working');
@@ -27,7 +28,10 @@ export function useChat() {
       try {
         const res = await fetch('/chat', {
           method: 'POST',
-        headers: { 'Content-Type': 'application/json' },
+          headers: {
+            'Content-Type': 'application/json',
+            ...(sessionToken !== null ? { Authorization: `Bearer ${sessionToken}` } : {}),
+          },
           body: JSON.stringify({ message: text }),
         });
         if (!res.ok) throw new Error('chat unavailable');
@@ -42,7 +46,9 @@ export function useChat() {
         setHeading(nextHeading);
       }
       setStatus('done');
-  }, []);
+    },
+    [sessionToken],
+  );
 
   return { messages, status, heading, send };
 }