Link test: download series (bulk sampled, warm bursts, paced) and burst-vs-idle; car results

Orin -> tablet over NCM: paced streams up to 4 MB/s are clean; unpaced
bursts and bulk hit multi-second holds that inflate the RTO to 10-16 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz

android/app/src/main/kotlin/dev/yukart/display/MainActivity.kt

@@ -22,7 +22,7 @@ import io.flutter.plugin.common.MethodChannel
  *   When asked, the whole process is bound to the Ethernet (NCM) network while it
  *   exists, and unbound when it goes.
  *
- * Also a development hook: `am start -n dev.yukart.display/.MainActivity --es linktest <label>[@<host>]`
+ * Also a development hook: `am start -n dev.yukart.display/.MainActivity --es linktest [dl:|bi:]<label>[@<host>]`
  * runs the link test (lib/linktest.dart) without touching the screen.
  */
 class MainActivity : FlutterActivity() {