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/chat-message-display.tsx

@@ -185,7 +185,8 @@ export function ChatMessageDisplay({
                 const validationError = validateMxCellStructure(replacedXML)
                 if (!validationError) {
                     previousXML.current = convertedXml
-                    onDisplayChart(replacedXML)
+                    // Skip validation in loadDiagram since we already validated above
+                    onDisplayChart(replacedXML, true)
                 } else {
                     console.log(
                         "[ChatMessageDisplay] XML validation failed:",