Add custom peer ID support to register method

- Update register() to accept optional customPeerId parameter
- Add TypeScript documentation with JSDoc comments
- Update README with usage examples and documentation
- Maintain backward compatibility with auto-generated IDs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/rondevu.ts

@@ -100,9 +100,10 @@ export class Rondevu {
 
   /**
    * Register and initialize authenticated client
+   * @param customPeerId - Optional custom peer ID (1-128 characters). If not provided, a random ID will be generated.
    */
-  async register(): Promise<Credentials> {
-    this.credentials = await this.auth.register();
+  async register(customPeerId?: string): Promise<Credentials> {
+    this.credentials = await this.auth.register(customPeerId);
 
     // Create offers API instance
     this._offers = new RondevuOffers(