fix: attendance admin — add user_name to records, fix Czech diacritics in table headers

- listAttendance() now maps users.first_name + last_name to user_name
- Fixed escaped Unicode in table headers (Zaměstnanec, Příchod, Poznámka)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/admin/components/AttendanceShiftTable.tsx

@@ -96,15 +96,15 @@ export default function AttendanceShiftTable({ records, onEdit, onDelete }: Atte
         <thead>
           <tr>
             <th>Datum</th>
-            <th>Zam\u011Bstnanec</th>
+            <th>Zaměstnanec</th>
             <th>Typ</th>
-            <th>P\u0159\u00EDchod</th>
+            <th>Příchod</th>
             <th>Pauza</th>
             <th>Odchod</th>
             <th>Hodiny</th>
             <th>Projekt</th>
             <th>GPS</th>
-            <th>Pozn\u00E1mka</th>
+            <th>Poznámka</th>
             <th>Akce</th>
           </tr>
         </thead>