feat(help-center): add more analytics integrations to portal settings

Adds Google Analytics 4, Hotjar, Plausible, Amplitude, Microsoft Clarity,
and Meta Pixel alongside Google Tag Manager. Provider IDs are stored in
portal config, validated against safe formats, and rendered as official
embed snippets on the public help center.

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

@@ -173,7 +173,14 @@ RSpec.describe 'Api::V1::Accounts::Portals', type: :request do
             ],
             'default_locale' => 'en',
             'layout' => 'classic',
-            'social_profiles' => {}
+            'social_profiles' => {},
+            'gtm_container_id' => nil,
+            'ga4_measurement_id' => nil,
+            'hotjar_site_id' => nil,
+            'plausible_domain' => nil,
+            'amplitude_api_key' => nil,
+            'clarity_project_id' => nil,
+            'meta_pixel_id' => nil
           }
         )
       end