fix: validate XML before displaying diagram to catch duplicate IDs (#147)

- Add validation to loadDiagram in diagram-context, returns error or null
- display_diagram and edit_diagram tools now check validation result
- Return error to AI agent with state: output-error so it can retry
- Skip validation for trusted sources (localStorage, history, internal templates)
- Add debug logging for tool call inputs to diagnose Bedrock API issues

components/history-dialog.tsx

@@ -32,7 +32,8 @@ export function HistoryDialog({
 
     const handleConfirmRestore = () => {
         if (selectedIndex !== null) {
-            onDisplayChart(diagramHistory[selectedIndex].xml)
+            // Skip validation for trusted history snapshots
+            onDisplayChart(diagramHistory[selectedIndex].xml, true)
             handleClose()
         }
     }