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

backend/backend_domains/experiments/ping_endpoint_v1.py

@@ -0,0 +1,9 @@
+# backend/api/endpoints/ping.py
+
+from fastapi import APIRouter
+
+router = APIRouter()
+
+@router.get("/")
+async def ping():
+    return {"message": "pong"}