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/widgets/info-button.html

@@ -1,8 +1,8 @@
 {{define "info-button"}}
 <!-- Info Button (Bottom Left) -->
 <button id="info-button" class="info-button no-print has-tooltip"
-        aria-label="{{if eq .Lang "es"}}Información{{else}}Information{{end}}"
-        data-tooltip="{{if eq .Lang "es"}}Información{{else}}Information{{end}}"
+        aria-label="{{.UI.Widgets.Info.AriaLabel}}"
+        data-tooltip="{{.UI.Widgets.Info.Tooltip}}"
         onclick="document.getElementById('info-modal').showModal()">
     <iconify-icon icon="mdi:information-outline" width="24" height="24"></iconify-icon>
 </button>