feat: Voice Channel (#11602)

Enables agents to initiate outbound calls and receive incoming calls
directly from the Chatwoot dashboard, with Twilio as the initial
provider.

Fixes:  #11481 

> This is an integration branch to ensure features works well and might
be often broken on down merges, we will be extracting the
functionalities via smaller PRs into develop

- [x] https://github.com/chatwoot/chatwoot/pull/11775
- [x] https://github.com/chatwoot/chatwoot/pull/12218
- [x] https://github.com/chatwoot/chatwoot/pull/12243
- [x] https://github.com/chatwoot/chatwoot/pull/12268
- [x] https://github.com/chatwoot/chatwoot/pull/12361
- [x]  https://github.com/chatwoot/chatwoot/pull/12782
- [x] #13064
- [ ] Ability for agents to join the inbound calls ( included in this PR
)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>
Co-authored-by: Pranav <pranav@chatwoot.com>

app/javascript/dashboard/api/channel/voice/voiceAPIClient.js

@@ -0,0 +1,40 @@
+/* global axios */
+import ApiClient from '../../ApiClient';
+import ContactsAPI from '../../contacts';
+
+class VoiceAPI extends ApiClient {
+  constructor() {
+    super('voice', { accountScoped: true });
+  }
+
+  // eslint-disable-next-line class-methods-use-this
+  initiateCall(contactId, inboxId) {
+    return ContactsAPI.initiateCall(contactId, inboxId).then(r => r.data);
+  }
+
+  leaveConference(inboxId, conversationId) {
+    return axios
+      .delete(`${this.baseUrl()}/inboxes/${inboxId}/conference`, {
+        params: { conversation_id: conversationId },
+      })
+      .then(r => r.data);
+  }
+
+  joinConference({ conversationId, inboxId, callSid }) {
+    return axios
+      .post(`${this.baseUrl()}/inboxes/${inboxId}/conference`, {
+        conversation_id: conversationId,
+        call_sid: callSid,
+      })
+      .then(r => r.data);
+  }
+
+  getToken(inboxId) {
+    if (!inboxId) return Promise.reject(new Error('Inbox ID is required'));
+    return axios
+      .get(`${this.baseUrl()}/inboxes/${inboxId}/conference/token`)
+      .then(r => r.data);
+  }
+}
+
+export default new VoiceAPI();