feat: Implement main application shell with navigation and color scheme toggle

- Added Appshell component with responsive navbar and main content area
- Integrated ColorSchemeToggle for light/dark mode switching
- Created Welcome component with styled title and introductory text
- Developed ChatPage for LLM interaction with WebSocket support
- Implemented Biblioteca for managing notes with rich text editor
- Added LoginPage for user authentication with error handling
- Introduced MessageList and MessageBubble components for chat messages
- Styled components with CSS modules for consistent design

frontend/src/frontend_domains/FitzStudio/Plantilla.tsx

@@ -0,0 +1,10 @@
+import { AppShellWithMenu } from './Appshell/Appshell';
+
+
+export function Plantilla() {
+  return (
+    <AppShellWithMenu>
+
+    </AppShellWithMenu>
+  );
+}