feat: add per-inbox toggle to disable incoming calls (#14645)

## Description

Adds a per-inbox "Allow incoming calls" toggle for voice-enabled
WhatsApp and Twilio inboxes. When turned off, the setting is persisted
on the channel; actually rejecting inbound calls is handled in a
follow-up PR.

## Type of change

- [ ] New feature (non-breaking change which adds functionality)

## Screenshot
<img width="804" height="384" alt="Screenshot 2026-06-04 at 11 44 07 AM"
src="https://github.com/user-attachments/assets/df8bb026-0387-4031-bcba-6d9a56872eb7"
/>


## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/api/inboxes.js

@@ -60,6 +60,12 @@ class Inboxes extends CacheEnabledApiClient {
   disableWhatsappCalling(inboxId) {
     return axios.post(`${this.url}/${inboxId}/disable_whatsapp_calling`);
   }
+
+  setInboundCalls(inboxId, enabled) {
+    return axios.post(`${this.url}/${inboxId}/set_inbound_calls`, {
+      inbound_calls_enabled: enabled,
+    });
+  }
 }
 
 export default new Inboxes();