Agregar botón de regreso a Inicio

Cambios:
- Agregar header con botón home en App.jsx
- Botón apunta a https://inicio.nucleoriofrio.com
- Estilos coherentes con diseño existente (gradiente morado/azul)
- Efectos hover y animaciones
- Responsive para móviles

El botón usa scope extensions para navegar dentro de la PWA.

src/App.css

@@ -253,21 +253,71 @@ button[type="submit"]:disabled {
   animation: slideIn 0.5s ease-out 0.1s;
 }
 
+.app-header {
+  display: flex;
+  justify-content: flex-end;
+  margin-bottom: 1.5rem;
+  animation: fadeIn 0.5s ease-out;
+}
+
+.home-button {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.7rem 1.5rem;
+  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
+  color: white;
+  text-decoration: none;
+  border-radius: 12px;
+  font-weight: 600;
+  font-size: 0.95rem;
+  transition: all 0.3s ease;
+  box-shadow: 0 4px 15px rgba(102, 126, 234, 0.3);
+  letter-spacing: 0.3px;
+  border: 1px solid rgba(255, 255, 255, 0.2);
+}
+
+.home-button:hover {
+  transform: translateY(-2px);
+  box-shadow: 0 6px 20px rgba(102, 126, 234, 0.5);
+  background: linear-gradient(135deg, #5a67d8 0%, #6b3fa0 100%);
+}
+
+.home-button:active {
+  transform: translateY(0);
+  box-shadow: 0 3px 10px rgba(102, 126, 234, 0.4);
+}
+
+.home-icon {
+  font-size: 1.1em;
+  display: inline-block;
+  transition: transform 0.3s ease;
+}
+
+.home-button:hover .home-icon {
+  transform: scale(1.2);
+}
+
 @media (max-width: 640px) {
   #root {
     padding: 1rem;
   }
-  
+
   .App {
     padding: 2rem 1.5rem;
   }
-  
+
   .form-container,
   .amigos-list {
     padding: 1.75rem;
   }
-  
+
   h1 {
     font-size: 2em;
   }
+
+  .home-button {
+    padding: 0.6rem 1.2rem;
+    font-size: 0.9rem;
+  }
 }

src/App.jsx

@@ -88,6 +88,12 @@ function App() {
 
   return (
     <div className="App">
+      <header className="app-header">
+        <a href="https://inicio.nucleoriofrio.com" className="home-button">
+          <span className="home-icon">🏠</span>
+          <span>Inicio</span>
+        </a>
+      </header>
       <h1>Registro de Amigos</h1>
       
       <form onSubmit={handleSubmit} className="form-container">