fix: correct PivotData memoization to detect data changes

**Root Cause Identified:**
- pivotDataKey only checked dataLength, not actual data changes
- Same length data (1000 records) resulted in no PivotData recreation
- Old data accumulated without cleanup for 800+ refreshes

**Fix:**
- Include actual data reference in pivotDataKey computation
- Now detects when new data array is generated (same length, different content)
- Forces PivotData recreation and cleanup on each refresh

**Expected Result:**
Memory should reset to baseline (~43MB) on each refresh instead of accumulating

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: Seungwoo321

src/components/pivottable-ui/VPivottableUi.vue

@@ -330,10 +330,10 @@ const unusedAttrs = computed(() => {
 })
 
 // Use computed with proper memoization to prevent unnecessary PivotData recreations
-// Only recreate when critical properties change
+// Include data reference to detect actual data changes, not just length
 const pivotDataKey = computed(() => 
   JSON.stringify({
-    dataLength: state.data?.length || 0,
+    dataReference: state.data, // Include actual data reference to detect changes
     rows: state.rows,
     cols: state.cols,
     vals: state.vals,