style(webui): polish composer, user bubble, and tool-call box

src/app/components/ChatInterface.tsx

@@ -2015,7 +2015,7 @@ export const ChatInterface = React.memo<ChatInterfaceProps>(
           )}
           <div
             className={cn(
-              "relative z-10 mx-auto mb-2 flex w-[calc(100%-16px)] max-w-[960px] flex-shrink-0 flex-col overflow-hidden rounded-xl border border-border bg-background transition-colors duration-200 ease-in-out sm:mb-4 sm:w-[calc(100%-24px)]",
+              "relative z-10 mx-auto mb-2 flex w-[calc(100%-16px)] max-w-[960px] flex-shrink-0 flex-col overflow-hidden rounded-2xl border border-border bg-background shadow-[var(--shadow-sm)] transition-colors duration-200 ease-in-out focus-within:border-[var(--brand)] focus-within:ring-2 focus-within:ring-[var(--brand)]/20 sm:mb-4 sm:w-[calc(100%-24px)]",
               "focus-within:ring-2 focus-within:ring-ring"
             )}
           >

src/app/components/ChatMessage.tsx

@@ -268,7 +268,7 @@ export const ChatMessage = React.memo<ChatMessageProps>(
                 className={cn(
                   "mt-4 overflow-hidden break-words text-sm font-normal leading-[150%]",
                   isUser
-                    ? "rounded-xl rounded-br-none border border-border px-3 py-2 text-foreground"
+                    ? "rounded-2xl rounded-br-md px-3.5 py-2 text-foreground"
                     : "text-primary"
                 )}
                 style={

src/app/components/ToolCallBox.tsx

@@ -302,7 +302,7 @@ export const ToolCallBox = React.memo<ToolCallBoxProps>(
                         return (
                           <div
                             key={key}
-                            className="rounded-sm border border-border"
+                            className="rounded-lg border border-border"
                           >
                             {isFoldable ? (
                               <button