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/auth.ts

@@ -29,14 +29,21 @@ export class RondevuAuth {
 
   /**
    * Register a new peer and receive credentials
+   * @param customPeerId - Optional custom peer ID (1-128 characters). If not provided, a random ID will be generated.
+   * @throws Error if registration fails (e.g., peer ID already in use)
    */
-  async register(): Promise<Credentials> {
+  async register(customPeerId?: string): Promise<Credentials> {
+    const body: { peerId?: string } = {};
+    if (customPeerId !== undefined) {
+      body.peerId = customPeerId;
+    }
+
     const response = await this.fetchFn(`${this.baseUrl}/register`, {
       method: 'POST',
       headers: {
         'Content-Type': 'application/json',
       },
-      body: JSON.stringify({}),
+      body: JSON.stringify(body),
     });
 
     if (!response.ok) {

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(