feat: update client to use service-based signaling endpoints

BREAKING CHANGE: Client API now uses service UUIDs for WebRTC signaling

- Replace answerOffer() with answerService()
- Replace getAnswer() with getServiceAnswer()
- Replace addIceCandidates() with addServiceIceCandidates()
- Replace getIceCandidates() with getServiceIceCandidates()
- Update RondevuSignaler to use service UUID instead of offer ID for signaling
- Automatically track offerId returned from service endpoints
- Bump version to 0.12.0

Matches server v0.4.0 service-based API refactor.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@xtr-dev/rondevu-client",
-  "version": "0.9.2",
+  "version": "0.12.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@xtr-dev/rondevu-client",
-      "version": "0.9.2",
+      "version": "0.12.0",
       "license": "MIT",
       "dependencies": {
         "@noble/ed25519": "^3.0.0",