refactor: Extract all hardcoded content to JSON files

- Move all bilingual text from templates to UI JSON (labels, buttons, modals)
- Move skills summary paragraph to CV JSON with HTML support
- Add new UI sections: navigation, viewControls, sections, footer, portfolio,
  pdfModal, shortcutsModal, infoModal, widgets
- Update Go structs to match expanded JSON structure
- Add template.HTML type for CV.SkillsSummary field
- Add JSON content validation test (70-json-content-validation.test.mjs)

Templates now contain only structural logic (CSS classes, HTML attributes)
while all user-visible text loads from JSON files for proper i18n support.

templates/cv-content.html

@@ -17,7 +17,7 @@
                 <details class="sidebar-accordion">
                     <summary class="sidebar-accordion-header">
                         <iconify-icon icon="mdi:brain" width="20" height="20"></iconify-icon>
-                        <span>{{if eq .Lang "es"}}Competencias Técnicas{{else}}Technical Skills{{end}}</span>
+                        <span>{{.UI.Sections.TechnicalSkills}}</span>
                         <iconify-icon icon="mdi:chevron-down" width="20" height="20" class="chevron"></iconify-icon>
                     </summary>
                     <div class="sidebar-accordion-content">
@@ -96,7 +96,7 @@
                 <details class="sidebar-accordion">
                     <summary class="sidebar-accordion-header">
                         <iconify-icon icon="mdi:brain" width="20" height="20"></iconify-icon>
-                        <span>{{if eq .Lang "es"}}Más Competencias{{else}}More Skills{{end}}</span>
+                        <span>{{.UI.Sections.MoreSkills}}</span>
                         <iconify-icon icon="mdi:chevron-down" width="20" height="20" class="chevron"></iconify-icon>
                     </summary>
                     <div class="sidebar-accordion-content">