fix(web): conversation DELETE — resolve Failed to fetch TypeError

Root cause: @fastify/cors default allowed methods are only GET, HEAD, POST
(CORS-safelisted methods). DELETE requires a CORS preflight OPTIONS request,
and without DELETE in Access-Control-Allow-Methods the browser rejects it
with TypeError: Failed to fetch before the request reaches the server.

Fix: explicitly set methods in enableCors() to include DELETE and all other
HTTP verbs used by the API.

Also add try/catch to handleDelete in ChatPage so errors surface in the
console rather than becoming unhandled promise rejections.

Fixes #195.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/gateway/src/main.ts

@@ -40,6 +40,7 @@ async function bootstrap(): Promise<void> {
   app.enableCors({
     origin: process.env['GATEWAY_CORS_ORIGIN'] ?? 'http://localhost:3000',
     credentials: true,
+    methods: ['GET', 'HEAD', 'POST', 'PUT', 'PATCH', 'DELETE', 'OPTIONS'],
   });
 
   await app.register(helmet as never, { contentSecurityPolicy: false });

apps/web/src/app/(dashboard)/chat/page.tsx

@@ -151,11 +151,15 @@ export default function ChatPage(): React.ReactElement {
 
   const handleDelete = useCallback(
     async (id: string) => {
-      await api<void>(`/api/conversations/${id}`, { method: 'DELETE' });
-      setConversations((prev) => prev.filter((c) => c.id !== id));
-      if (activeId === id) {
-        setActiveId(null);
-        setMessages([]);
+      try {
+        await api<void>(`/api/conversations/${id}`, { method: 'DELETE' });
+        setConversations((prev) => prev.filter((c) => c.id !== id));
+        if (activeId === id) {
+          setActiveId(null);
+          setMessages([]);
+        }
+      } catch (err) {
+        console.error('[ChatPage] Failed to delete conversation:', err);
       }
     },
     [activeId],