refactor: item 29 cleanup

F16 F17 F18 F19 F20 F21: import polling backs off and pauses in a hidden tab, one date format module, fake timers in the import tests, error codes instead of raw messages, one safe storage wrapper, dead code.

src/pages/AdminHintsPage.jsx

@@ -10,6 +10,7 @@ import {Input} from '@/components/ui/input';
 import {Label} from '@/components/ui/label';
 import {Textarea} from '@/components/ui/textarea';
 import HintCard from '../components/HintCard.jsx';
+import {formatDateTime} from '../utils/format.js';
 import PageContainer from '../components/PageContainer.jsx';
 import {createHint, endHint, fetchAdminHints} from '../utils/hints.js';
 import {MAX_HINT_LENGTH} from '../utils/limits.js';
@@ -94,7 +95,7 @@ export default function AdminHintsPage() {
     };
 
     const change = (field) => (event) => setForm({...form, [field]: event.target.value});
-    const formatDate = (value) => new Date(value).toLocaleString(i18n.language, {dateStyle: 'short', timeStyle: 'short'});
+    const formatDate = (value) => formatDateTime(value, i18n.language, {dateStyle: 'short', timeStyle: 'short'});
 
     if (status === 'forbidden') {
         return (