Restructure ESP32 firmware into modules, fix bugs, add tests

Structure (src/esp32/):
- logic/: DisplayController, schedule, power timer, LED pattern; pure C++
- display/: FlipdotFrames and bitmaps
- nano_link/: NanoLink (relay, serial, READY, bootloader) and flash bridge
- net/: WiFi/OTA/panic window, Home Assistant
- config.h with all settings; libs.h (globals in a header) removed

Bug fixes:
- Home Assistant switches now report their state back and start as ON
- loop() no longer blocks: WiFi.waitForConnectResult() (up to 60 s
  without WiFi) and getLocalTime() (5 s before NTP sync) were called
  every iteration
- Power switch off now powers off after 1 s even when a 30 s countdown
  is already running
- millis() overflow safe power-off timer; no frame catch-up bursts
- No garbage time string before NTP sync; 'Connecting...' stays instead
- Frames are only sent when the screen changes instead of every second
- Reset reasons are logged once instead of every 100 ms
- Removed dead code (unused fonts, WiFiMulti, rotated bitmap, ...)

Tests: new test_esp32 environment (26 tests); native renamed to test_nano

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

src/esp32/logic/display_controller.cpp

@@ -0,0 +1,118 @@
+#include "logic/display_controller.h"
+
+#include "config.h"
+#include "logic/schedule.h"
+
+DisplayController::DisplayController(DisplayPower &power, Frames &frames) : _power(power), _frames(frames)
+{
+}
+
+void DisplayController::setClockEnabled(bool enabled)
+{
+	_clock_enabled = enabled;
+}
+
+void DisplayController::setPowerEnabled(bool enabled)
+{
+	_power_enabled = enabled;
+}
+
+bool DisplayController::clockEnabled() const
+{
+	return _clock_enabled;
+}
+
+bool DisplayController::powerEnabled() const
+{
+	return _power_enabled;
+}
+
+void DisplayController::update(uint32_t now, bool time_valid, int hour, int minute)
+{
+	// Switched off elsewhere (power timer, Nano flashing): the Nano lost its frame
+	if (!_power.isOn())
+		_screen = Screen::Unknown;
+
+	if (_off_timer.expired(now))
+	{
+		_power.off();
+		_screen = Screen::Unknown;
+		return;
+	}
+
+	if (!_power_enabled)
+	{
+		if (_power.isOn())
+		{
+			_showBlank();
+			_off_timer.request(now, CLEAR_BEFORE_OFF_TIME);
+		}
+		return;
+	}
+
+	// Keep the boot screen until the time is known
+	if (!time_valid)
+		return;
+
+	if (!_clock_enabled)
+	{
+		// The logo is only shown while the display is on; it never switches the power on
+		if (_power.isOn())
+		{
+			_showLogo();
+			_off_timer.request(now, POWER_OFF_DELAY);
+		}
+		return;
+	}
+
+	switch (scheduleFor(hour, minute))
+	{
+	case ScheduleMode::Night:
+		if (_power.isOn())
+		{
+			_showBlank();
+			_off_timer.request(now, POWER_OFF_DELAY);
+		}
+		break;
+	case ScheduleMode::Clock:
+		_off_timer.cancel();
+		if (!_power.isOn())
+		{
+			_power.on();
+			_screen = Screen::Unknown;
+		}
+		_showClock(hour, minute);
+		break;
+	case ScheduleMode::Standby:
+		// Flipdots keep their image without power, so the last time stays visible
+		if (_power.isOn())
+			_off_timer.request(now, POWER_OFF_DELAY);
+		break;
+	}
+}
+
+void DisplayController::_showClock(int hour, int minute)
+{
+	if (_screen == Screen::Clock && _shown_hour == hour && _shown_minute == minute)
+		return;
+	_frames.clock(hour, minute);
+	_screen = Screen::Clock;
+	_shown_hour = hour;
+	_shown_minute = minute;
+}
+
+void DisplayController::_showLogo()
+{
+	if (_screen == Screen::Logo)
+		return;
+	_frames.logo();
+	_screen = Screen::Logo;
+}
+
+void DisplayController::_showBlank()
+{
+	if (_screen == Screen::Blank)
+		return;
+	_frames.blank();
+	_screen = Screen::Blank;
+}