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)

app/controllers/api/v1/accounts/onboardings_controller.rb

@@ -16,6 +16,10 @@ class Api::V1::Accounts::OnboardingsController < Api::V1::Accounts::BaseControll
     render 'api/v1/accounts/update', format: :json
   end
 
+  def help_center_generation
+    render json: help_center_generation_status
+  end
+
   private
 
   def finalizing_account_details?
@@ -33,4 +37,15 @@ class Api::V1::Accounts::OnboardingsController < Api::V1::Accounts::BaseControll
   def custom_attributes_params
     params.permit(:industry, :company_size, :timezone, :referral_source, :user_role, :website)
   end
+
+  def help_center_generation_status
+    {
+      generation_id: nil,
+      state: nil,
+      articles_count: 0,
+      categories_count: 0
+    }
+  end
 end
+
+Api::V1::Accounts::OnboardingsController.prepend_mod_with('Api::V1::Accounts::OnboardingsController')