feat: expose onboarding help center generation status (#14671)

This PR adds a reload-safe onboarding Help Center generation status
path. Previously, generation progress was pushed through ActionCable,
which meant the onboarding UI could lose context after a page reload or
missed websocket event. The new endpoint exposes the current generation
id, raw Redis generation state, and Help Center article/category counts
so clients can recover state by fetching from the backend.

**What changed**

- Added an onboarding Help Center generation status endpoint.
- Persisted `help_center_generation_id` when generation is enqueued.
- Removed Help Center generation ActionCable broadcasts completely.
- Kept generation progress in Redis as the backend source of truth.
- Kept Help Center generation out of the onboarding hot path; the
existing onboarding controller does not start generation yet.

**How to test**

1. Start Help Center generation for an account.
2. Fetch the onboarding generation status endpoint and verify it returns
the generation id, Redis state, and article/category counts.
3. Reload the onboarding UI or client state and fetch again to confirm
progress can be recovered without relying on websocket events.
4. Verify skipped/completed generation states are reflected from Redis.

## Related PRs

- https://github.com/chatwoot/chatwoot/pull/14569
- https://github.com/chatwoot/chatwoot/pull/14568
- https://github.com/chatwoot/chatwoot/pull/14567
- https://github.com/chatwoot/chatwoot/pull/14619
- https://github.com/chatwoot/chatwoot/pull/14565 (Primary onboarding
PR)

spec/controllers/api/v1/accounts/onboardings_controller_spec.rb

@@ -111,4 +111,40 @@ RSpec.describe 'Onboarding API', type: :request do
       end
     end
   end
+
+  describe 'GET /api/v1/accounts/{account.id}/onboarding/help_center_generation' do
+    context 'when unauthenticated' do
+      it 'returns unauthorized' do
+        get "/api/v1/accounts/#{account.id}/onboarding/help_center_generation", as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when authenticated as an agent (non-admin)' do
+      let(:agent) { create(:user, account: account, role: :agent) }
+
+      it 'returns unauthorized' do
+        get "/api/v1/accounts/#{account.id}/onboarding/help_center_generation",
+            headers: agent.create_new_auth_token, as: :json
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when no help center generation has started' do
+      it 'returns not_started with zero counts' do
+        get "/api/v1/accounts/#{account.id}/onboarding/help_center_generation",
+            headers: admin.create_new_auth_token, as: :json
+
+        expect(response).to have_http_status(:success)
+        expect(response.parsed_body).to include(
+          'generation_id' => nil,
+          'state' => nil,
+          'articles_count' => 0,
+          'categories_count' => 0
+        )
+      end
+    end
+  end
 end