revert: remove unnecessary prompt fallback from basic MaestroButton

The prompt={prompt || Object.values(...)} was added based on a wrong
assumption about the accordion form-submit bug. The real fix was
adding type='button' to the accordion toggles. This reverts the
Generator.tsx prompt prop back to just {prompt}.

frontend/src/components/Generator.tsx

@@ -186,7 +186,7 @@ export default function Generator({ onGenerate }: Props) {
             <div className="flex items-center justify-between mb-1.5">
               <label className="text-xs text-kithara-muted">Prompt</label>
               <MaestroButton
-                prompt={prompt || Object.values(structuredPrompt).filter(Boolean).join(' ')}
+                prompt={prompt}
                 onResult={(_result, _mode) => {
                   setPrompt(_result)
                   setError('')