feat(onboarding): add conversational ChatOnboarding component

frontend/src/App.jsx

@@ -5,6 +5,7 @@ import ProfilePage from './pages/ProfilePage'
 import ProgressPage from './pages/ProgressPage'
 import WorkoutPage from './pages/WorkoutPage'
 import WorkoutSelectPage from './pages/WorkoutSelectPage'
+import ChatOnboarding from './pages/ChatOnboarding'
 import './App.css'
 
 const API_URL = '/api'
@@ -21,6 +22,10 @@ function App() {
   const userId = user?.id || 1
   const today = new Date().toISOString().split('T')[0]
 
+  if (user && !user.onboarding_complete) {
+    return <ChatOnboarding />
+  }
+
   const fetchProgram = async () => {
     if (program) return // Already loaded
     try {