feat: Adiciona field type social_link para redes sociais do usuário

Implementa o field type 'social_link' com seletor de rede e URL de
perfil, composto por:

- SocialLinkItem: field type com colunas 'network' (varchar 64) e
  'url' (varchar 2048), cardinalidade ilimitada
- SocialLinkWidget: widget com select de rede e input de URL
- SocialLinkFormatter: formatter que renderiza links com classe CSS
  por rede (social-link--{network}), target _blank e rel noopener
- config/optional: field.storage e field.field para user
- config/translations/pt-br: tradução do label e description
- hook_install e update_10002: configura form/view displays
- UserInfoBlock: expõe social_links via getSocialLinks()
- Template: adiciona seção de redes sociais e remove referências
  obsoletas a category e dept_code
- translations/site_users.pt-br.po: strings do novo field type

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/optional/field.field.user.user.field_user_social_links.yml

@@ -0,0 +1,20 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.user.field_user_social_links
+  module:
+    - site_users
+    - user
+id: user.user.field_user_social_links
+field_name: field_user_social_links
+entity_type: user
+bundle: user
+label: 'Social Links'
+description: 'Social network profile links.'
+required: false
+translatable: false
+default_value: {}
+default_value_callback: ''
+settings: {}
+field_type: social_link

config/optional/field.storage.user.field_user_social_links.yml

@@ -0,0 +1,18 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - site_users
+    - user
+id: user.field_user_social_links
+field_name: field_user_social_links
+entity_type: user
+type: social_link
+settings: {}
+module: site_users
+locked: false
+cardinality: -1
+translatable: false
+indexes: {}
+persist_with_no_fields: false
+custom_storage: false