Fix shifted pictures: non-blocking Nano drawing, frame check, refresh settings

The Nano's periodic full redraw blocked for ~0.8 s. A frame that arrived
meanwhile overflowed its 64-byte serial buffer; lost bytes in a bitmap
shift the rest of the image (picture moved up), and diff frames never
repaired it.

- Nano: all drawing (frames, effects, the dot refresh) runs from update()
  in ~1 ms slices; the refresh pauses while a frame is received or shown
- New commands: C (reply with the image checksum) and I (refresh minutes,
  EEPROM)
- ESP32: NanoMonitor asks for the checksum after frames and sends the whole
  image again on a mismatch, missing answer or Nano restart; counts ERR
  replies. Periodic whole-image resync.
- Settings: "Dot refresh" and "Image resync" intervals (settings v5,
  v4 records are migrated)
- System tab: loop timing, free memory, frame check counts
- test_driver: the real driver against a simulated panel

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/esp32/app.cpp

@@ -25,6 +25,8 @@ BROSE9323 display(DISPLAY_WIDTH, DISPLAY_HEIGHT, PANEL_WIDTH);
 FlipdotFrames frames(display, pageResources);
 StatusScreen status(display, nano);
 DisplayController controller(nano, frames);
+LoopStats loopStats;
+NanoMonitor nanoMonitor(nano, display);
 
 static Settings settings;
 static bool restart_pending = false;
@@ -87,7 +89,7 @@ static void apply()
 {
 	controller.setSettings(settings.schedule, settings.clock);
 	controller.setEffectTime(effectTime(settings.drive));
-	status.setDrive(settings.flip_time, settings.drive);
+	status.setDrive(settings.flip_time, settings.drive, settings.refresh.dots);
 	frames.setDrive(settings.flip_time, settings.drive);
 	haApiSetSettings(settings.home_assistant);
 	applyOffPage();
@@ -137,7 +139,8 @@ const char *appSaveSettings(const Settings &new_settings, bool &restart_needed)
 	const DriveSettings &a = settings.drive, &b = new_settings.drive;
 	bool drive_changed = settings.flip_time != new_settings.flip_time || a.flip_gap != b.flip_gap ||
 						 a.pulses != b.pulses || a.effect != b.effect || a.effect_time != b.effect_time ||
-						 a.effect_small_only != b.effect_small_only;
+						 a.effect_small_only != b.effect_small_only ||
+						 settings.refresh.dots != new_settings.refresh.dots;
 	settings = new_settings;
 	saveSettings(settings);
 	selector.setChosen(settings.page);