feat(help-center): support per-locale portal title, name & header (#14642)

Portals can now override their name, page title and header text per
locale, with a fallback chain of locale override → default locale → base
value. Overrides are stored under portal.config.locale_translations and
validated with a JSON schema.

Editing is exposed as a "Localize content" action in each non-default
locale's menu on the Locale page, and all public-facing portal views
(classic + documentation layouts) render the localized values. The live
chat widget is also loaded in the active portal locale.


<img width="494" height="395" alt="Screenshot 2026-06-03 at 2 48 59 PM"
src="https://github.com/user-attachments/assets/e55a06e8-f20f-4d8a-9352-92fde28a9a19"
/>



https://github.com/user-attachments/assets/f5affbd2-7ad4-415a-b376-57c759fc2aaa

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/views/api/v1/accounts/portals/_portal.json.jbuilder

@@ -18,6 +18,7 @@ json.config do
   json.default_locale portal.default_locale
   json.layout portal.layout
   json.social_profiles portal.social_profiles
+  json.locale_translations portal.config['locale_translations'] || {}
 end
 
 if portal.channel_web_widget