feat: App shell with login, session sidebar, chat panel, right panel

- Create RightPanel component with browser/artifacts tab switching
- Replace App.tsx with 3-column layout (auth loading/login/app states)
- Replace main.tsx with globals.css import (remove index.css)
- Remove Vite template files (App.css, index.css, assets/react.svg)
- Fix LoginPage.tsx FormEvent type-only import for verbatimModuleSyntax
- Fix vite.config.ts to use vitest/config for proper test property typing
- Add tests: RightPanel (10 tests), App rendering states (7 tests)

frontend/src/App.tsx

@@ -1,121 +1,48 @@
-import { useState } from 'react'
-import reactLogo from './assets/react.svg'
-import viteLogo from './assets/vite.svg'
-import heroImg from './assets/hero.png'
-import './App.css'
+import { useAuth } from './hooks/useAuth'
+import { useSessions } from './hooks/useSessions'
+import { useChat } from './hooks/useChat'
+import { LoginPage } from './components/LoginPage'
+import { SessionSidebar } from './components/SessionSidebar'
+import { ChatPanel } from './components/ChatPanel'
+import { RightPanel } from './components/RightPanel'
 
 function App() {
-  const [count, setCount] = useState(0)
+  const { user, loading: authLoading, login, logout } = useAuth()
+  const { sessions, activeSessionId, createNew, switchTo, refresh } = useSessions()
+  const { messages, isStreaming, sendMessage } = useChat(activeSessionId)
+
+  if (authLoading) {
+    return (
+      <div className='login-page'>
+        <div style={{ color: '#8888aa' }}>Loading...</div>
+      </div>
+    )
+  }
+
+  if (!user) {
+    return <LoginPage onLogin={login} />
+  }
 
   return (
-    <>
-      <section id="center">
-        <div className="hero">
-          <img src={heroImg} className="base" width="170" height="179" alt="" />
-          <img src={reactLogo} className="framework" alt="React logo" />
-          <img src={viteLogo} className="vite" alt="Vite logo" />
-        </div>
-        <div>
-          <h1>Get started</h1>
-          <p>
-            Edit <code>src/App.tsx</code> and save to test <code>HMR</code>
-          </p>
-        </div>
-        <button
-          type="button"
-          className="counter"
-          onClick={() => setCount((count) => count + 1)}
-        >
-          Count is {count}
-        </button>
-      </section>
-
-      <div className="ticks"></div>
-
-      <section id="next-steps">
-        <div id="docs">
-          <svg className="icon" role="presentation" aria-hidden="true">
-            <use href="/icons.svg#documentation-icon"></use>
-          </svg>
-          <h2>Documentation</h2>
-          <p>Your questions, answered</p>
-          <ul>
-            <li>
-              <a href="https://vite.dev/" target="_blank">
-                <img className="logo" src={viteLogo} alt="" />
-                Explore Vite
-              </a>
-            </li>
-            <li>
-              <a href="https://react.dev/" target="_blank">
-                <img className="button-icon" src={reactLogo} alt="" />
-                Learn more
-              </a>
-            </li>
-          </ul>
-        </div>
-        <div id="social">
-          <svg className="icon" role="presentation" aria-hidden="true">
-            <use href="/icons.svg#social-icon"></use>
-          </svg>
-          <h2>Connect with us</h2>
-          <p>Join the Vite community</p>
-          <ul>
-            <li>
-              <a href="https://github.com/vitejs/vite" target="_blank">
-                <svg
-                  className="button-icon"
-                  role="presentation"
-                  aria-hidden="true"
-                >
-                  <use href="/icons.svg#github-icon"></use>
-                </svg>
-                GitHub
-              </a>
-            </li>
-            <li>
-              <a href="https://chat.vite.dev/" target="_blank">
-                <svg
-                  className="button-icon"
-                  role="presentation"
-                  aria-hidden="true"
-                >
-                  <use href="/icons.svg#discord-icon"></use>
-                </svg>
-                Discord
-              </a>
-            </li>
-            <li>
-              <a href="https://x.com/vite_js" target="_blank">
-                <svg
-                  className="button-icon"
-                  role="presentation"
-                  aria-hidden="true"
-                >
-                  <use href="/icons.svg#x-icon"></use>
-                </svg>
-                X.com
-              </a>
-            </li>
-            <li>
-              <a href="https://bsky.app/profile/vite.dev" target="_blank">
-                <svg
-                  className="button-icon"
-                  role="presentation"
-                  aria-hidden="true"
-                >
-                  <use href="/icons.svg#bluesky-icon"></use>
-                </svg>
-                Bluesky
-              </a>
-            </li>
-          </ul>
-        </div>
-      </section>
-
-      <div className="ticks"></div>
-      <section id="spacer"></section>
-    </>
+    <div className='app-layout'>
+      <SessionSidebar
+        sessions={sessions}
+        activeSessionId={activeSessionId}
+        onSelect={(id) => switchTo(id)}
+        onCreate={async () => {
+          await createNew()
+          await refresh()
+        }}
+        onLogout={logout}
+      />
+      <ChatPanel
+        messages={messages}
+        isStreaming={isStreaming}
+        onSend={sendMessage}
+        sessionId={activeSessionId}
+      />
+      <RightPanel sessionId={activeSessionId} />
+    </div>
   )
 }