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/display/status_screen.cpp

@@ -9,10 +9,11 @@ StatusScreen::StatusScreen(BROSE9323 &display, NanoLink &nano) : _display(displa
 {
 }
 
-void StatusScreen::setDrive(uint16_t flip_time, const DriveSettings &drive)
+void StatusScreen::setDrive(uint16_t flip_time, const DriveSettings &drive, uint16_t dot_refresh)
 {
 	_flip_time = flip_time;
 	_drive = drive;
+	_dot_refresh = dot_refresh;
 }
 
 void StatusScreen::sendDrive()
@@ -30,6 +31,7 @@ void StatusScreen::loop()
 	_display.setGap(_drive.flip_gap);
 	_display.setPulses(_drive.pulses);
 	_display.setEffect(_drive.effect, _drive.effect_time, _drive.effect_small_only ? EFFECT_FLAG_SMALL_ONLY : 0);
+	_display.setRefreshInterval(_dot_refresh);
 }
 
 void StatusScreen::show(const char *line1, const char *line2, bool keep_on)

src/esp32/display/status_screen.h

@@ -17,7 +17,7 @@ public:
 
 	// How the Nano drives the dots, sent with the first message (default: FLIP_TIME and
 	// the DriveSettings defaults, so the recovery app always shows its messages instantly)
-	void setDrive(uint16_t flip_time, const DriveSettings &drive);
+	void setDrive(uint16_t flip_time, const DriveSettings &drive, uint16_t dot_refresh = RefreshSettings().dots);
 	// Send them again (they changed), from loop()
 	void sendDrive();
 	// Sends changed drive settings once the display is on. Not while the Nano is flashed.
@@ -30,4 +30,5 @@ private:
 	bool _drive_pending = false;
 	uint16_t _flip_time;
 	DriveSettings _drive;
+	uint16_t _dot_refresh = RefreshSettings().dots;
 };