tablet error screen can recover from a stale bar_id; admin drink reorder gets a non-drag fallback

- App.tsx: the error screen (shown when api.config(barId) fails, e.g.
  an admin deleted/renamed the bar while this tablet was offline)
  only offered 'Neu laden', which re-reads the same stale localStorage
  bar_id and fails again — a permanent stuck loop with no in-app fix.
  Added a 'Bar wechseln' button reusing the existing changeBar()
  logic, which now also clears the error state.
- Admin.tsx BarDrinkEditor: the drag-and-drop reorder is a
  mouse-oriented API that doesn't fire on touch-only input and has no
  keyboard equivalent. Added ▲/▼ buttons alongside the drag handle so
  reordering works regardless of input method.

client/src/admin/Admin.tsx

@@ -322,6 +322,19 @@ function BarDrinkEditor({
             >
               <span class="grip" aria-hidden="true">⋮⋮</span>
               <span class="dnd-name">{idx + 1}. {d.name}</span>
+              {/* Drag-and-drop above doesn't fire on touch-only input (no
+                  mouse) and has no keyboard equivalent — these buttons are
+                  the fallback that works regardless of input method. */}
+              <button onClick={() => reorder(idx, idx - 1)} disabled={idx === 0} aria-label="nach oben">
+                ▲
+              </button>
+              <button
+                onClick={() => reorder(idx, idx + 1)}
+                disabled={idx === selected.length - 1}
+                aria-label="nach unten"
+              >
+                ▼
+              </button>
               <button onClick={() => remove(idx)}>×</button>
             </li>
           );

client/src/styles.css

@@ -295,4 +295,5 @@ button.danger { background: #5a2a2a; border-color: #7a3a3a; color: #fff; }
 .dnd-item.drop-target { border-color: #6aa; background: var(--surface-2); }
 .dnd-item .grip { opacity: 0.4; cursor: grab; user-select: none; }
 .dnd-item .dnd-name { flex: 1; }
+.dnd-item button { padding: 2px 8px; font-size: 13px; }
 .dnd-list li.muted { padding: 6px 8px; }

client/src/tablet/App.tsx

@@ -36,9 +36,24 @@ export function App() {
     localStorage.removeItem(STORAGE_KEY);
     setBarId(null);
     setConfig(null);
+    setError(null);
   }
 
-  if (error) return <div class="bar-picker"><h1>Fehler</h1><p>{error}</p><button onClick={() => location.reload()}>Neu laden</button></div>;
+  if (error) {
+    return (
+      <div class="bar-picker">
+        <h1>Fehler</h1>
+        <p>{error}</p>
+        <button onClick={() => location.reload()}>Neu laden</button>
+        {/* A stuck-forever loop is otherwise possible here: the stored bar_id
+            can be permanently invalid (e.g. an admin deleted/renamed the bar
+            while this tablet was offline), and "Neu laden" alone re-reads
+            that same stale id and fails again. Route back through the same
+            changeBar() the working UI uses, which clears it. */}
+        <button onClick={changeBar}>Bar wechseln</button>
+      </div>
+    );
+  }
   if (barId == null) return <BarPicker bars={bars} onPick={pick} />;
   if (!config) return <div class="bar-picker"><p>Lade…</p></div>;
   return <Sale config={config} onChangeBar={changeBar} />;