feat(account): persist signup attribution (#14761)

This keeps Chatwoot-side attribution persistence intentionally small and
Enterprise-only.

The website owns attribution capture, normalization, and source
classification. Chatwoot Cloud only reads the already-shaped first-party
attribution cookies during the current web signup account creation path
and stores the decoded payload in internal account metadata. Self-hosted
installs remain unchanged in this repo.

## What changed

- Added Enterprise-only attribution persistence to the current Cloud web
signup account creation path.
- Stores attribution only when `ChatwootApp.chatwoot_cloud?` is true.
- Reads the existing first-touch and last-touch attribution cookies.
- Saves only the documented scalar attribution fields under account
internal metadata.
- Preserves raw attribution values and leaves escaping to display
boundaries.
- Bounds stored attribution values to the website field-size limit.
- Keeps OSS controller code unchanged.
- Keeps signup attribution request coverage in Enterprise specs.
- Avoids backend attribution derivation, referrer parsing, or fallback
classification.
- Skips authenticated add-workspace flows so additional workspaces are
not counted as signup attribution.
- Does not hook unused account creation paths or OmniAuth account
creation.

## How to test

- `bundle exec rubocop
spec/controllers/api/v1/accounts_controller_spec.rb
spec/enterprise/controllers/api/v1/accounts_controller_spec.rb
enterprise/app/controllers/enterprise/api/v1/accounts_settings.rb
enterprise/app/services/internal/accounts/marketing_attribution_service.rb
spec/enterprise/services/internal/accounts/marketing_attribution_service_spec.rb`
- `bundle exec rspec spec/controllers/api/v1/accounts_controller_spec.rb
spec/enterprise/controllers/api/v1/accounts_controller_spec.rb
spec/enterprise/services/internal/accounts/marketing_attribution_service_spec.rb`
- On a cloud-like setup, create an account through the current web
signup path with attribution cookies and confirm account internal
metadata is populated.
- On a non-cloud setup or authenticated add-workspace flow, confirm
account-create behavior is unchanged and no attribution is stored.

enterprise/app/controllers/enterprise/api/v1/accounts_settings.rb

@@ -1,6 +1,20 @@
 module Enterprise::Api::V1::AccountsSettings
+  def create
+    super
+    record_marketing_attribution
+  end
+
   private
 
+  def record_marketing_attribution
+    return if current_user.present?
+    return if @account.blank?
+
+    Internal::Accounts::MarketingAttributionService.new(account: @account, cookies: cookies).perform
+  rescue StandardError => e
+    ChatwootExceptionTracker.new(e).capture_exception
+  end
+
   def permitted_settings_attributes
     super + [{ conversation_required_attributes: [] }]
   end