fix: prevent [object Object] rendering in 25 frontend components

Replace direct {error} JSX rendering with typeof check + .message fallback.
When error is an object (not a string), React showed [object Object].
Now renders error.message or fallback string.

frontend/src/pages/SettingsSequences.tsx

@@ -115,7 +115,7 @@ export function SettingsSequencesPage() {
         </button>
       </div>
 
-      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{error}</div>}
+      {error && <div className="p-3 text-sm text-red-700 bg-red-50 rounded-lg">{typeof error === "string" ? error : (error as any)?.message || "Ein Fehler ist aufgetreten"}</div>}
 
       {showForm && (
         <form onSubmit={handleSubmit(onSubmit)} className="p-4 border border-secondary-200 rounded-lg space-y-3">