admin: unify response error extraction into errText helper

removes a double-body-read in the delete handlers and makes the four
alert sites consistent.

client/src/admin/Admin.tsx

@@ -6,6 +6,15 @@ async function j<T = any>(res: Response): Promise<T> {
   return res.json();
 }
 
+// Best-effort error message from a failed response ({ error } JSON or status text).
+async function errText(res: Response): Promise<string> {
+  try {
+    return (await res.json()).error ?? res.statusText;
+  } catch {
+    return res.statusText;
+  }
+}
+
 interface Drink { id: number; name: string; price_cents: number; archived: number }
 interface BarRow { id: number; name: string; pfand_cents: number; drink_ids: number[] }
 interface Totals { bar_id: number; bar_name: string; tx_count: number; paid_cents: number; crew_count: number; pfand_returns: number }
@@ -189,7 +198,7 @@ function Drinks() {
   async function del(d: Drink) {
     if (!confirm(`Getränk „${d.name}“ wirklich löschen?`)) return;
     const res = await fetch(`/admin/api/drinks/${d.id}`, { method: 'DELETE' });
-    if (!res.ok) { alert(`Fehler: ${(await res.json().catch(() => null))?.error ?? await res.text()}`); return; }
+    if (!res.ok) { alert(`Fehler: ${await errText(res)}`); return; }
     reload();
   }
 
@@ -337,14 +346,14 @@ function Bars() {
       headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify(body),
     });
-    if (!res.ok) alert(`Fehler: ${await res.text()}`);
+    if (!res.ok) alert(`Fehler: ${await errText(res)}`);
     reload();
   }
 
   async function delBar(b: BarRow) {
     if (!confirm(`Tresen „${b.name}“ wirklich löschen?`)) return;
     const res = await fetch(`/admin/api/bars/${b.id}`, { method: 'DELETE' });
-    if (!res.ok) { alert(`Fehler: ${(await res.json().catch(() => null))?.error ?? await res.text()}`); return; }
+    if (!res.ok) { alert(`Fehler: ${await errText(res)}`); return; }
     reload();
   }
 
@@ -357,7 +366,7 @@ function Bars() {
       body: JSON.stringify({ name, pfand_cents: 200 }),
     });
     if (!res.ok) {
-      alert(`Fehler: ${await res.text()}`);
+      alert(`Fehler: ${await errText(res)}`);
       return;
     }
     setNewName('');