Fix getCategory to use set_hst for proper categorization

Tags are now categorized based on their set_hst field, which
points to the parent category tag (e.g., hst, spe, vue, vsn, msn).
This uses the actual semantic relationship defined in the database
rather than inferring from ref prefix or using the base.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.html

@@ -846,8 +846,16 @@ const Utils = {
   },
 
   getCategory(tag) {
-    // Category is determined by the current base being viewed
-    return State.get("base");
+    // Category is determined by the tag's set_hst (parent category MRF)
+    const setHst = tag.set_hst;
+    if (!setHst) return State.get("base");
+
+    // Look up the category tag in hstTags
+    const hstTags = State.get("hstTags");
+    const categoryTag = hstTags.find(t => t.mrf === setHst);
+
+    // Return the ref of the category tag, or fall back to base
+    return categoryTag?.ref || State.get("base");
   },
 
   updateHash() {