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/partials/modals/info-modal.html

@@ -3,7 +3,7 @@
 <dialog id="info-modal" class="info-modal no-print"
         _="on click call closeOnBackdrop(me, event)">
     <div class="info-modal-content">
-        <button class="info-modal-close" onclick="document.getElementById('info-modal').close()" aria-label="Close">
+        <button class="info-modal-close" onclick="document.getElementById('info-modal').close()" aria-label="{{.UI.PdfModal.Close}}">
             <iconify-icon icon="mdi:close" width="24" height="24"></iconify-icon>
         </button>