fix(tui): drain Kitty key release events before exit to prevent SSH leak

Adds Terminal.prepareForExit() to disable Kitty protocol and wait for
in-flight release events before fully stopping. This prevents escape
sequences from leaking to the parent shell over slow SSH connections.

Fixes #1204

packages/tui/test/virtual-terminal.ts

@@ -36,6 +36,10 @@ export class VirtualTerminal implements Terminal {
 		this.xterm.write("\x1b[?2004h");
 	}
 
+	async prepareForExit(_drainMs?: number): Promise<void> {
+		// No-op for virtual terminal - no Kitty protocol to drain
+	}
+
 	stop(): void {
 		// Disable bracketed paste mode
 		this.xterm.write("\x1b[?2004l");