Fix multiple connect events and add leave method

- Add hasConnected flag to prevent duplicate connect events
- Add leave() method to RondevuConnection to end sessions
- Add leave() API method to call /leave endpoint
- Version 0.3.5

The connect event will now only fire once per connection,
fixing the issue where it could fire multiple times as the
WebRTC connectionState transitions.

The leave() method allows either peer to end the session
by deleting the offer from the server.

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

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

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@xtr-dev/rondevu-client",
-  "version": "0.3.4",
+  "version": "0.3.5",
   "description": "TypeScript client for Rondevu peer signaling and discovery server",
   "type": "module",
   "main": "dist/index.js",