feat(cli): add bell() utility for terminal attention requests

Write ASCII BEL character to stdout when running in a TTY.
Causes dock bounce on macOS, taskbar flash on Windows,
and urgency hint on Linux.

packages/opencode/src/kilocode/bell.ts

@@ -0,0 +1,6 @@
+// kilocode_change - new file
+export function bell() {
+  if (process.stdout.isTTY) {
+    process.stdout.write("\x07")
+  }
+}