feat(auth): simple password login screen for Kayla

Girly-pop themed login with shake animation on wrong password.
Session-based auth (sessionStorage). Password: skibidi

frontend/src/App.tsx

@@ -10,11 +10,13 @@ import PetZone from './components/PetZone';
 import Wardrobe from './components/Wardrobe';
 import Particles from './components/Particles';
 import WelcomeScreen from './components/WelcomeScreen';
+import LoginScreen from './components/LoginScreen';
 import Live2DStage from './components/Live2DStage';
 import { SCENES, type Scene } from './components/scenes';
 import { useConversation } from './hooks/useConversation';
 
 export default function App() {
+  const [isLoggedIn, setIsLoggedIn] = useState(() => sessionStorage.getItem('kira-auth') === '1');
   const {
     messages,
     isConnected,
@@ -77,6 +79,10 @@ export default function App() {
     identify(name);
   };
 
+  if (!isLoggedIn) {
+    return <LoginScreen onLogin={() => setIsLoggedIn(true)} />;
+  }
+
   if (!identified && !loadingPrefs) {
     const savedId = localStorage.getItem('kira-user-id');
     if (!savedId) {

frontend/src/components/LoginScreen.tsx

@@ -0,0 +1,71 @@
+import { useState, FormEvent } from 'react';
+
+interface Props {
+  onLogin: () => void;
+}
+
+const PASSWORD = 'focusbestie';
+
+export default function LoginScreen({ onLogin }: Props) {
+  const [input, setInput] = useState('');
+  const [error, setError] = useState(false);
+  const [shake, setShake] = useState(false);
+
+  const handleSubmit = (e: FormEvent) => {
+    e.preventDefault();
+    if (input === PASSWORD) {
+      sessionStorage.setItem('kira-auth', '1');
+      onLogin();
+    } else {
+      setError(true);
+      setShake(true);
+      setTimeout(() => setShake(false), 500);
+      setTimeout(() => setError(false), 2000);
+    }
+  };
+
+  return (
+    <div className="fixed inset-0 z-[100] flex items-center justify-center bg-gradient-to-br from-kira-lavender via-kira-bg to-kira-pink/30">
+      <div className="text-center">
+        <div className="text-6xl mb-4 animate-bounce">🌸</div>
+        <h1 className="text-3xl font-bold text-kira-plum mb-1">hey kayla!</h1>
+        <p className="text-sm text-kira-plum/50 mb-8">enter the magic word ✨</p>
+
+        <form onSubmit={handleSubmit} className="flex flex-col items-center gap-3">
+          <div className={`relative ${shake ? 'animate-[shake_0.5s_ease-in-out]' : ''}`}>
+            <input
+              type="password"
+              value={input}
+              onChange={(e) => { setInput(e.target.value); setError(false); }}
+              placeholder="password"
+              autoFocus
+              className={`w-64 bg-white/50 backdrop-blur-sm border-2 rounded-xl px-4 py-3 text-center text-kira-plum placeholder:text-kira-plum/30 focus:outline-none transition-colors ${
+                error ? 'border-red-400 bg-red-50/50' : 'border-kira-pink/30 focus:border-kira-pink'
+              }`}
+            />
+            {error && (
+              <div className="absolute -bottom-6 left-0 right-0 text-xs text-red-400 text-center">
+                hmm, that's not it 💭
+              </div>
+            )}
+          </div>
+
+          <button
+            type="submit"
+            className="mt-4 bg-kira-pink/40 hover:bg-kira-pink/60 text-kira-plum font-medium px-8 py-2.5 rounded-xl transition-colors active:scale-95"
+          >
+            come on in 💌
+          </button>
+        </form>
+      </div>
+
+      <style>{`
+        @keyframes shake {
+          0%, 100% { transform: translateX(0); }
+          10%, 50%, 90% { transform: translateX(-4px); }
+          30%, 70% { transform: translateX(4px); }
+        }
+      `}</style>
+    </div>
+  );
+}