feat(KB-166): fix search reset bug in dependency dropdown

- Fix search input resetting when selecting dependencies in PlanningModeModal
- Remove obsolete changeset file fix-planning-modal-autostart.md
- Update PlanningModeModal tests for the fixed behavior
- Add focus management improvements in TaskDetailModal

packages/dashboard/app/components/TaskDetailModal.tsx

@@ -131,6 +131,13 @@ export function TaskDetailModal({
     setIsEditing(false);
   }, [task.id, task.title, task.description]);
 
+  // Reset dependency search when dropdown closes
+  useEffect(() => {
+    if (!showDepDropdown) {
+      setDepSearch("");
+    }
+  }, [showDepDropdown]);
+
   // Auto-focus title when entering edit mode
   useEffect(() => {
     if (isEditing) {