feat: update interests templates for category-based data model

Interests are now grouped by category (matching skills pattern).
Updated cv-interests.njk to iterate categories, cv.js fallback to {},
and cv.njk hasCvData check to include interests.

cv.njk

@@ -10,7 +10,8 @@ pagefindIgnore: true
 
 {% set hasCvData = (cv.experience and cv.experience.length) or
       (cv.projects and cv.projects.length) or
-      (cv.skills and ((cv.skills or {}) | dictsort | length)) %}
+      (cv.skills and ((cv.skills or {}) | dictsort | length)) or
+      (cv.interests and ((cv.interests or {}) | dictsort | length)) %}
 
 {% if hasCvData %}