Add content translations for site_sections taxonomy terms

Taxonomy term names are content, not interface strings, so .po files
don't translate them. This adds programmatic content translations via
the ContentLanguageSettings API and addTranslation/setName on each term.

- Add _structural_pages_term_translations() with pt-br name map
- Add _structural_pages_add_term_translations() to create/update translations
- Add _structural_pages_ensure_content_translation() using ContentLanguageSettings API
- Add config/optional for new installs with content_translation enabled
- Remove term name entries from .po file (ineffective for content)
- Add update hook 10004 to fix existing installations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

config/optional/language.content_settings.taxonomy_term.site_sections.yml

@@ -0,0 +1,17 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - taxonomy.vocabulary.site_sections
+  module:
+    - content_translation
+    - taxonomy
+id: taxonomy_term.site_sections
+target_entity_type_id: taxonomy_term
+target_bundle: site_sections
+default_langcode: site_default
+language_alterable: true
+content_translation_enabled: true
+third_party_settings:
+  content_translation:
+    enabled: true