Rename module site_structure → structural_pages and vocabulary site_section → site_sections

Renames the module from site_structure to structural_pages and pluralizes
the taxonomy vocabulary machine name from site_section to site_sections,
updating all config, PHP, translations, and documentation references
while preserving field_site_section, clears_site_section, and $site_section_id.

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

config/install/pathauto.pattern.site_sections_term.yml

@@ -0,0 +1,20 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - structural_pages
+    - taxonomy
+id: site_sections_term
+label: 'Site Sections Term'
+type: 'canonical_entities:taxonomy_term'
+pattern: '[term:hierarchy-path]'
+selection_logic: and
+selection_criteria:
+  d5fc9eaf-f3e6-6cg6-1f00-414817610285:
+    id: entity_bundle:taxonomy_term
+    negate: false
+    context_mapping:
+      taxonomy_term: taxonomy_term
+    bundles:
+      site_sections: site_sections
+weight: 0