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/Welcome/Welcome.tsx

@@ -0,0 +1,22 @@
+import { Anchor, Text, Title } from '@mantine/core';
+import classes from './Welcome.module.css';
+import { useMantineTheme } from '@mantine/core';
+
+export function Welcome() {
+
+  const theme = useMantineTheme();
+
+  return (
+    <>
+      <Title className={classes.title} ta="center" mt={100}>
+        Hola! {' '}
+        <Text inherit variant="gradient" component="span" gradient={{ from: theme.colors.brand[7], to: theme.colors.secondary[4], }} style={{ letterSpacing: '1px' }}>
+          Holooooo
+        </Text>
+      </Title>
+      <Text c="dimmed" ta="left" size="lg" maw={580} mx="auto" mt="xl">
+        Lorem ipsum dolor sit amet consectetur adipisicing elit. Suscipit modi officia porro natus ullam vero mollitia provident, fuga quidem! Perspiciatis explicabo, vel non illum libero suscipit esse animi a voluptatem!
+      </Text>
+    </>
+  );
+}