fix: improve VLM validation with bug fixes and i18n

- Fix race condition in pendingValidationRef (reject previous pending validation)
- Fix response format consistency (use streaming for all responses)
- Remove dead code (unused lastRequestRef and ValidationRequest interface)
- Consolidate duplicate types (re-export from validation-schema.ts)
- Add 'success_with_warnings' status for valid diagrams with warnings
- Fix tool card auto-collapse (only collapse once, respect user toggle)
- Set VLM validation default to disabled
- Add i18n support for diagram validation settings (en/zh/ja)
- Mark feature as experimental in settings UI

hooks/use-diagram-tool-handlers.ts

@@ -325,9 +325,13 @@ ${finalXml}
                             }
 
                             // Notify UI of success (include the image)
+                            // Use "success_with_warnings" if valid but has issues
+                            const hasWarnings = result.issues.length > 0
                             updateValidationState(
                                 toolCall.toolCallId,
-                                "success",
+                                hasWarnings
+                                    ? "success_with_warnings"
+                                    : "success",
                                 { result, imageData: capturedPngData },
                             )
                         }

hooks/use-validate-diagram.ts

@@ -26,11 +26,6 @@ interface UseValidateDiagramOptions {
     onError?: (error: Error) => void
 }
 
-interface ValidationRequest {
-    imageData: string
-    sessionId?: string
-}
-
 // Track pending validation promises for imperative API
 type PendingValidation = {
     resolve: (result: ValidationResult) => void
@@ -40,7 +35,6 @@ type PendingValidation = {
 export function useValidateDiagram(options: UseValidateDiagramOptions = {}) {
     const { onSuccess, onError } = options
     const pendingValidationRef = useRef<PendingValidation | null>(null)
-    const lastRequestRef = useRef<ValidationRequest | null>(null)
 
     const { object, submit, isLoading, error, stop } = useObject({
         api: getApiEndpoint("/api/validate-diagram"),
@@ -87,8 +81,13 @@ export function useValidateDiagram(options: UseValidateDiagramOptions = {}) {
             imageData: string,
             sessionId?: string,
         ): Promise<ValidationResult> => {
-            // Store request for potential retry
-            lastRequestRef.current = { imageData, sessionId }
+            // Reject any pending validation to prevent promise leaks
+            if (pendingValidationRef.current) {
+                pendingValidationRef.current.reject(
+                    new Error("Validation superseded by new request"),
+                )
+                pendingValidationRef.current = null
+            }
 
             return new Promise((resolve, reject) => {
                 // Store the promise handlers