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.

README.md

@@ -0,0 +1,99 @@
+# Zui
+
+Node-based editor (React Flow) for configs, variables, and rendering (PlantUML, Markdown, etc.). Optional Node.js backend API for demos or future features (e.g. todos CRUD).
+
+## Project layout
+
+```
+my-app/
+├── frontend/           # React app (Vite, TypeScript)
+│   ├── Dockerfile      # Multi-stage for prod (build → Nginx)
+│   ├── Dockerfile.dev  # Dev with hot reload
+│   ├── src/
+│   ├── public/
+│   ├── nginx.conf
+│   └── package.json
+├── backend/            # Node.js/Express API
+│   ├── Dockerfile
+│   ├── src/
+│   │   └── index.js
+│   └── package.json
+├── docker-compose.yml
+├── .dockerignore
+└── .gitignore
+```
+
+Ignored by git: `node_modules`, `dist`, `.env`, `.env.*` (see [.gitignore](.gitignore)). Local Docker overrides: `docker-compose.override.yml` (optional, not committed).
+
+---
+
+## Run locally (dev)
+
+**Frontend only:**
+
+```bash
+cd frontend && npm install && npm run dev
+# → http://localhost:3000
+```
+
+**Frontend + backend** (so the app can show “Backend API: N todos”):
+
+```bash
+# Terminal 1 – backend
+cd backend && npm install && npm run dev
+# → http://localhost:8080
+
+# Terminal 2 – frontend
+cd frontend && npm install && npm run dev
+# → http://localhost:3000 (Vite proxies /api/todos to backend)
+```
+
+---
+
+## Run with Docker
+
+```bash
+docker compose up --build
+```
+
+- **Frontend**: http://localhost:3000 (Nginx; `/api/*` proxied to backend).
+- **Backend**: http://localhost:8080 (Express).
+
+Environment variables (backend service):
+
+| Variable     | Default                    | Description |
+|-------------|----------------------------|-------------|
+| `PORT`      | `8080`                     | Backend listen port. |
+| `CORS_ORIGIN` | `http://localhost:3000`  | Allowed origin for CORS. |
+
+For self-hosting (e.g. Tailscale/HTTPS): set `CORS_ORIGIN` to your frontend URL; put Caddy or Nginx in front for TLS if needed.
+
+**Dev with Docker (frontend hot reload):** use `frontend/Dockerfile.dev` and mount `./frontend` as a volume, or run `cd frontend && npm run dev` locally.
+
+---
+
+## Scripts
+
+| Command | Description |
+|--------|-------------|
+| `cd frontend && npm run dev` | Vite dev server. |
+| `cd frontend && npm run build` | Build frontend for production. |
+| `cd frontend && npm run preview` | Preview production build. |
+| `cd backend && npm run dev` | Backend with `--watch`. |
+| `cd backend && npm start` | Backend production run. |
+| `docker compose up --build` | Run frontend + backend in Docker. |
+
+---
+
+## Backend API (no DB)
+
+| Method | Path | Description |
+|--------|------|-------------|
+| GET    | `/api/todos`     | List all todos. |
+| GET    | `/api/todos/:id` | Get one todo. |
+| POST   | `/api/todos`     | Create (`{ "title": "...", "completed": false }`). |
+| PUT    | `/api/todos/:id` | Update. |
+| DELETE | `/api/todos/:id` | Delete. |
+| GET    | `/health`        | Health check (e.g. for Docker). |
+
+Data is in-memory (resets on restart). Add a JSON file or DB later if needed.