feat(GRO-106): portal Communication tab — real backend

- Added GET /portal/conversation and GET /portal/conversation/messages endpoints
- Created Communication.api.ts with typed fetchers and React hooks
- Rewired Communication.tsx to use real API, removed mock data
- Added composer-disabled bar with "Reply from your phone" tooltip
- Added conversation route tests to portal.test.ts

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

apps/web/src/portal/CustomerPortal.tsx

@@ -170,7 +170,7 @@ export function CustomerPortal() {
       case "billing":
         return <BillingPayments readOnly={!!isReadOnly} sessionId={sessionId} />;
       case "messages":
-        return <Communication readOnly={!!isReadOnly} />;
+        return <Communication readOnly={!!isReadOnly} sessionId={sessionId} />;
       case "settings":
         return <AccountSettings readOnly={!!isReadOnly} sessionId={sessionId} />;
     }