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/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; }