fix(chat): prevent chatbox jump when sending first message

The ChatInput wrapper toggled between pb-8 (empty state) and pb-4
(has messages), causing a 16px vertical jump the moment hasMessages
flipped. EmptyState already centers itself inside flex-1, so the
extra padding wasn't needed — collapse to a single pb-4.

packages/views/chat/components/chat-page.tsx

@@ -256,12 +256,7 @@ export function ChatPage() {
           <EmptyState agentName={activeAgent?.name} onPickPrompt={handleSend} />
         )}
 
-        <div
-          className={cn(
-            "mx-auto w-full max-w-3xl pb-4",
-            hasMessages ? "" : "pb-8",
-          )}
-        >
+        <div className="mx-auto w-full max-w-3xl pb-4">
           <ChatInput
             onSend={handleSend}
             onStop={handleStop}