fix: add validation error handling to InactiveJailDetail

- Add validationError state to show network/API failures to user
- Use handleFetchError to properly handle auth errors (suppress generic error banner, trigger session-expiry flow)
- Clear validationError when user clicks Validate again
- Ensure error MessageBar renders instead of success banner when validation fails
- Fix InactiveJailDetail onValidate to return Promise as expected by prop type
- Fix useJailConfigs test to use correct JailConfig interface

Fixes TASK-BUG-05: prevents silent validation failures where user cannot distinguish between clean 'no issues' result and server error.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

frontend/src/components/config/JailsTab.tsx

@@ -32,6 +32,7 @@ import {
   Play24Regular,
 } from "@fluentui/react-icons";
 import { ApiError } from "../../api/client";
+import { handleFetchError } from "../../utils/fetchError";
 import type {
   AddLogPathRequest,
   BackendType,
@@ -651,13 +652,17 @@ function InactiveJailDetail({
   const styles = useConfigStyles();
   const [validating, setValidating] = useState(false);
   const [validationResult, setValidationResult] = useState<JailValidationResult | null>(null);
+  const [validationError, setValidationError] = useState<string | null>(null);
 
   const handleValidate = useCallback((): void => {
     setValidating(true);
     setValidationResult(null);
+    setValidationError(null);
     onValidate()
       .then((result) => { setValidationResult(result); })
-      .catch(() => { /* validation call failed — ignore */ })
+      .catch((err: unknown) => {
+        handleFetchError(err, setValidationError, "Validation request failed.");
+      })
       .finally(() => { setValidating(false); });
   }, [onValidate]);
 
@@ -700,8 +705,17 @@ function InactiveJailDetail({
         <Input readOnly value={jail.source_file} className={styles.codeFont} />
       </Field>
 
+      {/* Validation error panel */}
+      {validationError !== null && (
+        <div style={{ marginBottom: tokens.spacingVerticalM }}>
+          <MessageBar intent="error">
+            <MessageBarBody>{validationError}</MessageBarBody>
+          </MessageBar>
+        </div>
+      )}
+
       {/* Validation result panel */}
-      {validationResult !== null && (
+      {validationResult !== null && validationError === null && (
         <div style={{ marginBottom: tokens.spacingVerticalM }}>
           {blockingIssues.length === 0 && advisoryIssues.length === 0 ? (
             <MessageBar intent="success">
@@ -924,7 +938,7 @@ export function JailsTab({ initialJail }: JailsTabProps): React.JSX.Element {
                   ? (): void => { void handleDeactivateInactive(selectedInactiveJail.name); }
                   : undefined
               }
-              onValidate={() => { void validateJailConfig(selectedInactiveJail.name); }}
+              onValidate={async () => validateJailConfig(selectedInactiveJail.name)}
             />
           ) : null}
         </ConfigListDetail>