fix: add unsaved changes banners to edit mode forms

Adds amber edit-mode banners to AppConfigDetailPage and both
DefaultResourcesSection/JarRetentionSection in EnvironmentsPage,
matching the existing ConfigSubTab pattern.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/pages/Admin/AppConfigDetailPage.tsx

@@ -317,6 +317,12 @@ export default function AppConfigDetailPage() {
         )}
       </div>
 
+      {editing && (
+        <div className={styles.editBanner}>
+          Editing configuration. Changes are not saved until you click Save.
+        </div>
+      )}
+
       <div className={styles.header}>
         <h2 className={styles.title}><MonoText size="md">{appId}</MonoText></h2>
         <div className={styles.meta}>