fix: render drag handle character literal instead of unicode escape

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mbreiser

experiment_designer.html

@@ -848,7 +848,7 @@
 
         /* Drag handle indicator on condition blocks */
         .timeline-block.condition::before {
-            content: '\u2807';
+            content: '⠇';
             position: absolute;
             top: 2px;
             left: 4px;