style(newwhats): painel de agentes +20% no desktop e tela cheia no mobile

Painel do meio (selecionar agente) passa de 280px para 336px (md:) e, no mobile,
ocupa a tela (flex-1) com o painel principal oculto (hidden md:flex).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/views/newwhats/SecretariaView.tsx

@@ -1625,8 +1625,8 @@ export function SecretariaView(props: { onNavigate?: (view: string) => void } =
         />
       )}
 
-      {/* Left Panel */}
-      <div className="w-[280px] h-full bg-white border-r border-gray-100 flex flex-col shrink-0">
+      {/* Left Panel — no mobile ocupa a tela (flex-1); no desktop 336px (+20%) */}
+      <div className="flex-1 md:flex-none md:w-[336px] h-full bg-white border-r border-gray-100 flex flex-col">
 
         {/* Agent selector */}
         <div className="border-b border-gray-100 shrink-0">
@@ -1696,8 +1696,8 @@ export function SecretariaView(props: { onNavigate?: (view: string) => void } =
         )}
       </div>
 
-      {/* Main Panel */}
-      <div className="flex-1 flex flex-col h-full overflow-hidden">
+      {/* Main Panel — oculto no mobile (painel lateral vira tela cheia) */}
+      <div className="hidden md:flex flex-1 flex-col h-full overflow-hidden">
         {store.selectedConversation && activeTab === 'conversations' ? (
           <ChatArea
             conversation={store.selectedConversation}