fix: ensure mode switch icon maintains consistent size

- Changed PocketKnife icon from className="w-4" to className="size-4"
- This ensures both width and height are set to prevent icon shrinking
- Aligns with TerminalSquare icon implementation for consistency

Author: roomote

webview-ui/src/components/chat/ChatRow.tsx

@@ -754,7 +754,7 @@ export const ChatRowContent = ({
 				return (
 					<>
 						<div style={headerStyle}>
-							<PocketKnife className="w-4" aria-label="Switch mode icon" />
+							<PocketKnife className="size-4" aria-label="Switch mode icon" />
 							<span style={{ fontWeight: "bold" }}>
 								{message.type === "ask" ? (
 									<>