Add external API integration for wiki/web UI synchronization

This commit adds a comprehensive external API system that allows external tools
(wikis, web UIs, etc.) to control and synchronize with Fantasy Map Generator.

New Features:
- External API Bridge (modules/external-api.js)
  - Event-driven architecture with EventEmitter
  - Map lifecycle control (create, load, save)
  - Data access methods (rivers, cultures, states, burgs)
  - Data mutation methods with auto-redraw
  - Export support (SVG, PNG, JSON)
  - Change detection with automatic event emission

- PostMessage Communication Layer
  - Auto-enables when FMG is embedded in iframe
  - Bidirectional message passing
  - Request/response pattern with promise support
  - Automatic event forwarding to parent window

- REST API Server (api-server/)
  - Express.js server with full CRUD operations
  - WebSocket support via Socket.IO for real-time updates
  - File upload support for map and CSV import
  - In-memory storage (can be replaced with database)
  - CORS enabled for cross-origin requests
  - Comprehensive endpoints for all map data

- Client Library (api-server/client.js)
  - Simple JavaScript client for REST API
  - Promise-based async methods
  - Works in browser and Node.js

- Demo Pages (demos/)
  - PostMessage integration demo with full UI
  - REST API demo with interactive testing
  - WebSocket demo for real-time events

- Documentation
  - Comprehensive integration guide (EXTERNAL_API_INTEGRATION.md)
  - API reference with TypeScript interfaces
  - Multiple integration examples
  - Troubleshooting guide

Integration Methods:
1. PostMessage Bridge - For iframe embedding
2. REST API - For server-side integration
3. Direct JavaScript API - For same-origin apps

Use Cases:
- Wiki pages that need to display and control maps
- Web UIs that want to edit map data
- External tools that need to sync with FMG
- Real-time collaborative map editing
- Batch operations and automation

Technical Details:
- Zero dependencies for external-api.js (pure JS)
- Auto-initializes on DOMContentLoaded
- Throttled change detection (500ms debounce)
- Deep cloning for data access (prevents mutations)
- Error handling throughout
- Version tagged (v1.0.0)

Updated Files:
- index.html: Added script tag to load external-api module

All APIs are backward compatible and don't affect existing functionality.

api-server/README.md

@@ -0,0 +1,233 @@
+# Fantasy Map Generator - REST API Server
+
+A Node.js/Express server that provides REST API endpoints and WebSocket support for the Fantasy Map Generator.
+
+## Features
+
+- ✅ RESTful API with full CRUD operations
+- ✅ WebSocket support for real-time updates
+- ✅ Map storage and management
+- ✅ CSV import for rivers and other data
+- ✅ Export support (SVG, PNG, JSON)
+- ✅ CORS enabled for cross-origin requests
+- ✅ File upload support
+
+## Quick Start
+
+### Installation
+
+```bash
+npm install
+```
+
+### Run Server
+
+```bash
+# Production
+npm start
+
+# Development (with auto-reload)
+npm run dev
+```
+
+Server will start on `http://localhost:3000`
+
+## API Documentation
+
+Visit `http://localhost:3000` after starting the server to see the full API documentation.
+
+### Quick Examples
+
+#### Create a Map
+
+```bash
+curl -X POST http://localhost:3000/api/maps \
+  -H "Content-Type: application/json" \
+  -d '{"seed": "my-world"}'
+```
+
+Response:
+```json
+{
+  "success": true,
+  "mapId": "map_1234567890_abc123",
+  "message": "Map creation initiated",
+  "pollUrl": "/api/maps/map_1234567890_abc123"
+}
+```
+
+#### Get Map Data
+
+```bash
+curl http://localhost:3000/api/maps/map_1234567890_abc123
+```
+
+#### Update Rivers
+
+```bash
+curl -X PUT http://localhost:3000/api/maps/map_1234567890_abc123/rivers \
+  -H "Content-Type: application/json" \
+  -d '{"rivers": [{"i":1,"name":"Mystic River","type":"River"}]}'
+```
+
+#### Import Rivers from CSV
+
+```bash
+curl -X POST http://localhost:3000/api/maps/map_1234567890_abc123/rivers/import \
+  -F "file=@rivers.csv"
+```
+
+## WebSocket
+
+### Connect
+
+```javascript
+import { io } from 'socket.io-client';
+
+const socket = io('http://localhost:3000');
+
+socket.on('connect', () => {
+  console.log('Connected!');
+});
+```
+
+### Events
+
+**Server Events (listen):**
+- `map:creating` - Map creation started
+- `map:created` - Map creation completed
+- `map:updated` - Map data updated
+- `map:deleted` - Map deleted
+- `rivers:updated` - Rivers updated
+- `rivers:imported` - Rivers imported from CSV
+- `burg:added` - New burg added
+
+**Client Events (emit):**
+- `map:update` - Update map data
+- `map:created` - Notify map creation complete
+- `export:completed` - Export completed
+
+## Configuration
+
+### Environment Variables
+
+```bash
+# Port (default: 3000)
+PORT=3000
+```
+
+### Storage
+
+By default, maps are stored in memory. For production, replace the `Map` with a database:
+
+```javascript
+// Replace this in server.js
+const maps = new Map();
+
+// With this (example with MongoDB)
+const maps = await db.collection('maps');
+```
+
+## Deployment
+
+### Docker
+
+```dockerfile
+FROM node:18
+WORKDIR /app
+COPY package*.json ./
+RUN npm install
+COPY . .
+EXPOSE 3000
+CMD ["npm", "start"]
+```
+
+Build and run:
+```bash
+docker build -t fmg-api .
+docker run -p 3000:3000 fmg-api
+```
+
+### Production Considerations
+
+1. **Database**: Replace in-memory storage with MongoDB, PostgreSQL, etc.
+2. **Authentication**: Add JWT or OAuth for protected endpoints
+3. **Rate Limiting**: Add express-rate-limit
+4. **Validation**: Add input validation with joi or express-validator
+5. **Logging**: Add morgan or winston
+6. **Monitoring**: Add health checks and metrics
+
+## Architecture
+
+```
+Client (Browser/Wiki)
+    ↓
+REST API / WebSocket
+    ↓
+Server (Express + Socket.IO)
+    ↓
+Storage (In-memory Map / Database)
+```
+
+## Dependencies
+
+- **express**: Web framework
+- **socket.io**: WebSocket server
+- **cors**: Cross-origin resource sharing
+- **multer**: File upload handling
+- **body-parser**: Request body parsing
+
+## Development
+
+### Add New Endpoint
+
+```javascript
+// In server.js
+app.get('/api/maps/:id/custom', async (req, res) => {
+  try {
+    const {id} = req.params;
+    // Your logic here
+    res.json({success: true, data: {}});
+  } catch (error) {
+    res.status(500).json({success: false, error: error.message});
+  }
+});
+```
+
+### Add WebSocket Event
+
+```javascript
+// In server.js
+io.on('connection', (socket) => {
+  socket.on('custom:event', (data) => {
+    // Handle event
+    io.emit('custom:response', data);
+  });
+});
+```
+
+## Testing
+
+### Manual Testing
+
+Use the demo pages:
+- REST API: `http://localhost:3000/demos/rest-api-demo.html`
+- WebSocket: `http://localhost:3000/demos/websocket-demo.html`
+
+### Automated Testing
+
+```bash
+# Install test dependencies
+npm install --save-dev mocha chai supertest
+
+# Run tests
+npm test
+```
+
+## License
+
+MIT - Same as Fantasy Map Generator
+
+## Support
+
+For issues and questions, see the main repository.