feat: add node help system and registry for extensible node types

- Implemented a help system for different node types (config, render, variable, function) with detailed usage instructions.
- Created a node registry to manage node types, including registration, retrieval, and validation of connections between nodes.
- Defined central node and edge types for the application to streamline state management.
- Added Nunjucks autocomplete functionality to enhance user experience in template editing.
- Developed a syntax highlighting parser for PlantUML and Nunjucks within the CodeMirror editor.
- Registered built-in node types at application startup, including their default configurations and help entries.
- Introduced a theme context provider to manage light/dark mode preferences across the application.
- Created utility functions for class name management using clsx and tailwind-merge.
- Set up Tailwind CSS for styling with custom themes and responsive design.
- Configured Vite for development with proxy settings for backend API calls and Kroki diagram service.

frontend/src/main.tsx

@@ -0,0 +1,17 @@
+import React from 'react'
+import { createRoot } from 'react-dom/client'
+import App from './App'
+import { ThemeProvider } from './lib/themeContext'
+import { registerBuiltinNodes } from './lib/registerBuiltinNodes'
+import './styles.css'
+import '@xyflow/react/dist/style.css'
+
+registerBuiltinNodes()
+
+createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <ThemeProvider>
+      <App />
+    </ThemeProvider>
+  </React.StrictMode>
+)