Fix JS cache busting and store selectedField in segment stats callback

The imupath.js version string in the HTML was stale (20260125b), so
browsers kept serving a cached copy that lacked the time/distance
ranking key fix. Bumped to 20260131 to force a fresh fetch.

Also ensured appState.selectedField is set in the AJAX success
callback so getSegmentRanking() uses the correct key when looking
up rankings for built-in fields like time and distance.

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

Author: DocGarbanzo

donkeycar/parts/web_controller/templates/imupath.html

@@ -422,6 +422,6 @@
   </div>
 </div>
 
-<script src="/static/imupath.js?v=20260125b"></script>
+<script src="/static/imupath.js?v=20260131"></script>
 </body>
 </html>

donkeycar/parts/web_controller/templates/static/imupath.js

@@ -261,6 +261,7 @@ function computeSegmentStatistics() {
     dataType: 'json',
     success: function(response) {
       appState.segmentRankings = response.rankings || null;
+      appState.selectedField = fieldName;  // Store for getSegmentRanking()
       $('#stats-spinner').hide();
 
       // Refresh display