fix(data-editor): insert new columns next to their group instead of at end

- Use findLastIndex to locate existing group members and splice after them
- Fixes filtering panel showing new columns detached from their group
- Apply same fix in export header rebuild path (io.js)

Author: Mnikley

src/managers/io.js

@@ -1506,7 +1506,13 @@ class IOManager {
         (h) => h.subGroup === elem.subGroup && h.key === elem.key,
       );
       if (!exists) {
-        targetList.push(elem);
+        // Insert next to existing group members to keep groups contiguous
+        const lastGroupIdx = targetList.findLastIndex(h => h.subGroup === subGroup);
+        if (lastGroupIdx !== -1) {
+          targetList.splice(lastGroupIdx + 1, 0, elem);
+        } else {
+          targetList.push(elem);
+        }
       }
     }
 

src/utilities/data_editor.js

@@ -851,11 +851,14 @@ class DataTable {
         return;
       }
 
-      // Add to appropriate data headers list
-      if (isNodeProperty) {
-        this.fileData.nodeDataHeaders.push({ subGroup: groupName, key: propertyName });
+      // Add to appropriate data headers list, inserting next to existing group members
+      const targetHeaders = isNodeProperty ? this.fileData.nodeDataHeaders : this.fileData.edgeDataHeaders;
+      const lastGroupIdx = targetHeaders.findLastIndex(h => h.subGroup === groupName);
+      const newHeader = { subGroup: groupName, key: propertyName };
+      if (lastGroupIdx !== -1) {
+        targetHeaders.splice(lastGroupIdx + 1, 0, newHeader);
       } else {
-        this.fileData.edgeDataHeaders.push({ subGroup: groupName, key: propertyName });
+        targetHeaders.push(newHeader);
       }
 
       // Reload tab data to rebuild headers with proper filtering