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/models/channel/twilio_sms.rb

@@ -12,6 +12,7 @@
 #  medium                         :integer          default("sms")
 #  messaging_service_sid          :string
 #  phone_number                   :string
+#  provider_config                :jsonb
 #  twiml_app_sid                  :string
 #  voice_enabled                  :boolean          default(FALSE), not null
 #  created_at                     :datetime         not null
@@ -54,6 +55,11 @@ class Channel::TwilioSms < ApplicationRecord
     medium == 'sms' ? 'Twilio SMS' : 'Whatsapp'
   end
 
+  # Mutes only the incoming side of calling; default on, so only an explicit false disables inbound.
+  def inbound_calls_enabled?
+    provider_config['inbound_calls_enabled'] != false
+  end
+
   def send_message(to:, body:, media_url: nil)
     params = send_message_from.merge(to: to, body: body)
     params[:media_url] = media_url if media_url.present?

app/models/channel/whatsapp.rb

@@ -49,6 +49,11 @@ class Channel::Whatsapp < ApplicationRecord
       account.feature_enabled?('channel_voice')
   end
 
+  # Mutes only the incoming side of calling; default on, so only an explicit false disables inbound.
+  def inbound_calls_enabled?
+    provider_config['inbound_calls_enabled'] != false
+  end
+
   # Whether this inbox can do WhatsApp calling at all. Meta's Calling API is
   # reachable by any whatsapp_cloud inbox, so 360dialog inboxes can't be toggled
   # on even though calling_enabled would persist.