feat: show processing status for one-off campaigns (#14592)

## Summary

One-off SMS and WhatsApp campaigns now show a `Processing` state while
the audience send is in progress. The campaign moves to `Completed`
after processing finishes, and already-processing campaigns are skipped
by the scheduler to avoid duplicate sends.

## Closes

- [CW-6037: feat: Introduce an in-progress status for
campaigns](https://linear.app/chatwoot/issue/CW-6037/feat-introduce-an-in-progress-status-for-campaigns)

## Screenshot

SMS campaign card showing the new `Processing` status.

<img width="3840" height="2160" alt="framed-campaign-processing-status"
src="https://github.com/user-attachments/assets/de7913b5-65fb-4121-9034-24a568eb0382"
/>

## What changed

- Added `processing` as a campaign status.
- Mark one-off campaigns as `processing` under a row lock before the
send service runs.
- Complete SMS, Twilio SMS, and WhatsApp one-off campaigns after
audience processing finishes.
- Keep campaigns in `processing` if an unexpected service error escapes,
so the scheduler does not automatically resend the audience.
- Added the `Processing` label for SMS and WhatsApp campaign cards.

## Known operational behavior

If a worker is interrupted or an unexpected service error escapes after
a campaign is marked `processing`, the campaign can remain in
`processing`. This is intentional for now to avoid automatic
full-audience resends. Installation admins can decide whether to mark
the campaign completed or restart it manually from the Rails console
after checking what was sent.

## How to test

- Create a one-off SMS or WhatsApp campaign scheduled for now.
- Run the scheduled job or trigger the campaign job.
- Confirm the campaign card shows `Processing` while the audience is
being processed. For small audiences, refresh during processing or use a
larger audience so the state is observable.
- Confirm the campaign moves to `Completed` after audience processing
finishes.
- Confirm an already-processing campaign is not enqueued again by the
scheduled job.

spec/models/campaign_spec.rb

@@ -83,6 +83,38 @@ RSpec.describe Campaign do
         campaign.save!
         campaign.trigger!
       end
+
+      it 'marks the campaign as processing before triggering the service' do
+        campaign.save!
+        sms_service = double
+
+        expect(Twilio::OneoffSmsCampaignService).to receive(:new).with(campaign: campaign).and_return(sms_service)
+        expect(sms_service).to receive(:perform) do
+          expect(campaign.reload.processing?).to be true
+        end
+
+        campaign.trigger!
+      end
+
+      it 'does not trigger a processing campaign again' do
+        campaign.save!
+        campaign.processing!
+
+        expect(Twilio::OneoffSmsCampaignService).not_to receive(:new)
+
+        campaign.trigger!
+      end
+
+      it 'keeps the campaign processing when triggering fails' do
+        campaign.save!
+        sms_service = double
+
+        expect(Twilio::OneoffSmsCampaignService).to receive(:new).with(campaign: campaign).and_return(sms_service)
+        expect(sms_service).to receive(:perform).and_raise(StandardError, 'provider error')
+
+        expect { campaign.trigger! }.to raise_error(StandardError, 'provider error')
+        expect(campaign.reload.processing?).to be true
+      end
     end
 
     context 'when SMS campaign' do
@@ -107,6 +139,22 @@ RSpec.describe Campaign do
       end
     end
 
+    context 'when WhatsApp campaign feature is disabled' do
+      let(:account) { create(:account) }
+      let(:whatsapp_channel) do
+        create(:channel_whatsapp, account: account, provider: 'whatsapp_cloud', validate_provider_config: false, sync_templates: false)
+      end
+      let(:campaign) { create(:campaign, account: account, inbox: whatsapp_channel.inbox) }
+
+      it 'does not mark the campaign as processing' do
+        expect(Whatsapp::OneoffCampaignService).not_to receive(:new)
+
+        campaign.trigger!
+
+        expect(campaign.reload.active?).to be true
+      end
+    end
+
     context 'when Website campaign' do
       let(:campaign) { build(:campaign) }