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/tailwind.config.cjs

@@ -0,0 +1,57 @@
+/* Tailwind configuration for Vite + React */
+module.exports = {
+  darkMode: ['class'],
+  content: ['./index.html', './src/**/*.{ts,tsx,js,jsx}'],
+  theme: {
+    extend: {
+      borderRadius: {
+        lg: 'var(--radius)',
+        md: 'calc(var(--radius) - 2px)',
+        sm: 'calc(var(--radius) - 4px)'
+      },
+      colors: {
+        background: 'hsl(var(--background))',
+        foreground: 'hsl(var(--foreground))',
+        card: {
+          DEFAULT: 'hsl(var(--card))',
+          foreground: 'hsl(var(--card-foreground))'
+        },
+        popover: {
+          DEFAULT: 'hsl(var(--popover))',
+          foreground: 'hsl(var(--popover-foreground))'
+        },
+        primary: {
+          DEFAULT: 'hsl(var(--primary))',
+          foreground: 'hsl(var(--primary-foreground))'
+        },
+        secondary: {
+          DEFAULT: 'hsl(var(--secondary))',
+          foreground: 'hsl(var(--secondary-foreground))'
+        },
+        muted: {
+          DEFAULT: 'hsl(var(--muted))',
+          foreground: 'hsl(var(--muted-foreground))'
+        },
+        accent: {
+          DEFAULT: 'hsl(var(--accent))',
+          foreground: 'hsl(var(--accent-foreground))'
+        },
+        destructive: {
+          DEFAULT: 'hsl(var(--destructive))',
+          foreground: 'hsl(var(--destructive-foreground))'
+        },
+        border: 'hsl(var(--border))',
+        input: 'hsl(var(--input))',
+        ring: 'hsl(var(--ring))',
+        chart: {
+          '1': 'hsl(var(--chart-1))',
+          '2': 'hsl(var(--chart-2))',
+          '3': 'hsl(var(--chart-3))',
+          '4': 'hsl(var(--chart-4))',
+          '5': 'hsl(var(--chart-5))'
+        }
+      }
+    }
+  },
+  plugins: [require('tailwindcss-animate')],
+}