Move username and sign out below sidebar title

Username and 'Sign out' link now sit on their own row under the
Dataflow title, so they always have room to display regardless of
title width.

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

ui/src/App.jsx

@@ -18,23 +18,25 @@ const NAV = [
 
 export default function App() {
   const [authed, setAuthed] = useState(false)
+  const [loginUser, setLoginUser] = useState('')
   const [sources, setSources] = useState([])
   const [source, setSource] = useState(() => localStorage.getItem('selectedSource') || '')
   const [sidebarOpen, setSidebarOpen] = useState(false)
 
   async function handleLogin(user, pass) {
     setCredentials(user, pass)
-    // Verify credentials by hitting the API — throws on 401
     await api.getSources().then(s => {
       setSources(s)
       if (!source && s.length > 0) setSource(s[0].name)
       setAuthed(true)
+      setLoginUser(user)
     })
   }
 
   function handleLogout() {
     clearCredentials()
     setAuthed(false)
+    setLoginUser('')
     setSources([])
   }
 
@@ -57,12 +59,15 @@ export default function App() {
   const sidebar = (
     <div className="flex flex-col h-full">
       {/* Header */}
-      <div className="px-4 py-4 border-b border-gray-200 flex items-center justify-between">
+      <div className="px-4 py-3 border-b border-gray-200">
+        <div className="flex items-center justify-between">
           <span className="text-sm font-semibold text-gray-800 tracking-wide uppercase">Dataflow</span>
-        <div className="flex items-center gap-2">
-          <button onClick={handleLogout} className="text-xs text-gray-400 hover:text-gray-600 leading-none" title="Sign out">⏻</button>
           <button onClick={() => setSidebarOpen(false)} className="md:hidden text-gray-400 hover:text-gray-600 leading-none" title="Close">✕</button>
         </div>
+        <div className="flex items-center justify-between mt-1">
+          <span className="text-xs text-gray-400">{loginUser}</span>
+          <button onClick={handleLogout} className="text-xs text-gray-400 hover:text-red-500" title="Sign out">Sign out</button>
+        </div>
       </div>
 
       {/* Source selector */}