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/net/home_assistant.cpp

@@ -0,0 +1,55 @@
+#include "net/home_assistant.h"
+
+#include <ArduinoHA.h>
+#include <WiFi.h>
+
+#include "config.h"
+#include "credentials.h"
+
+static WiFiClient client;
+static HADevice device(HA_DEVICE_ID, sizeof(HA_DEVICE_ID));
+static HAMqtt mqtt(client, device);
+
+// Unique ids: do not change, Home Assistant's entities are linked to them
+static HASwitch clockSwitch("FlipDotDisplayClock");
+static HASwitch powerSwitch("FlipDotDisplayPower");
+
+static DisplayController *displayController = nullptr;
+
+// The switches are not optimistic: the new state must be reported back to Home Assistant
+static void onClockCommand(bool state, HASwitch *sender)
+{
+	displayController->setClockEnabled(state);
+	sender->setState(state);
+}
+
+static void onPowerCommand(bool state, HASwitch *sender)
+{
+	displayController->setPowerEnabled(state);
+	sender->setState(state);
+}
+
+void homeAssistantBegin(DisplayController &controller)
+{
+	displayController = &controller;
+
+	device.setName(HA_DEVICE_NAME);
+	device.setSoftwareVersion(HA_SOFTWARE_VERSION);
+
+	clockSwitch.setName("FlipDot Display Clock");
+	clockSwitch.setIcon("mdi:lightbulb");
+	clockSwitch.setCurrentState(controller.clockEnabled());
+	clockSwitch.onCommand(onClockCommand);
+
+	powerSwitch.setName("FlipDot Display Power");
+	powerSwitch.setIcon("mdi:lightbulb");
+	powerSwitch.setCurrentState(controller.powerEnabled());
+	powerSwitch.onCommand(onPowerCommand);
+
+	mqtt.begin(BROKER_ADDR, MQTT_USER, MQTT_PASSWORD);
+}
+
+void homeAssistantLoop()
+{
+	mqtt.loop();
+}

src/esp32/net/home_assistant.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "logic/display_controller.h"
+
+// Home Assistant integration over MQTT (with discovery). Two switches:
+//   FlipDot Display Clock  on = clock, off = Nintendo logo
+//   FlipDot Display Power  off = clear the display and switch it off
+void homeAssistantBegin(DisplayController &controller);
+void homeAssistantLoop();

src/esp32/net/wifi_ota.cpp

@@ -0,0 +1,70 @@
+#include "net/wifi_ota.h"
+
+#include <ArduinoOTA.h>
+#include <WiFi.h>
+#include <rom/rtc.h>
+
+#include "config.h"
+#include "credentials.h"
+
+void wifiBegin()
+{
+	WiFi.setHostname(HOSTNAME);
+	WiFi.mode(WIFI_STA);
+	WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+	Serial.println("Connecting to WiFi");
+	if (WiFi.waitForConnectResult() != WL_CONNECTED)
+	{
+		Serial.println("WiFi connection failed, restarting");
+		delay(5000);
+		ESP.restart();
+	}
+	// Later disconnects are handled by the WiFi driver's auto reconnect
+	Serial.print("Connected, IP ");
+	Serial.println(WiFi.localIP());
+}
+
+bool wifiConnected()
+{
+	return WiFi.status() == WL_CONNECTED;
+}
+
+void otaBegin()
+{
+	ArduinoOTA.setHostname(HOSTNAME);
+	ArduinoOTA.onStart([]() { Serial.println("OTA update started"); });
+	ArduinoOTA.onEnd([]() { Serial.println("OTA update done"); });
+	ArduinoOTA.onError([](ota_error_t error) { Serial.printf("OTA error %u\n", error); });
+	ArduinoOTA.begin();
+}
+
+void otaLoop()
+{
+	ArduinoOTA.handle();
+}
+
+// A normal start is a power on of CPU 0 or a start of CPU 1 by CPU 0
+static bool unexpectedReset()
+{
+	RESET_REASON cpu0 = rtc_get_reset_reason(0);
+	RESET_REASON cpu1 = rtc_get_reset_reason(1);
+	Serial.printf("Reset reason: CPU0 %d, CPU1 %d\n", cpu0, cpu1);
+	return cpu0 != POWERON_RESET && cpu1 != EXT_CPU_RESET;
+}
+
+void otaPanicWindow(int led_pin)
+{
+	if (!unexpectedReset())
+		return;
+
+	Serial.println("Unexpected reset: waiting for an OTA update");
+	uint32_t start = millis();
+	while (millis() - start < OTA_PANIC_WINDOW)
+	{
+		ArduinoOTA.handle();
+		// fast blink
+		digitalWrite(led_pin, (millis() / 50) % 2);
+		delay(10);
+	}
+	digitalWrite(led_pin, LOW);
+}

src/esp32/net/wifi_ota.h

@@ -0,0 +1,14 @@
+#pragma once
+
+// Connect to WiFi. Restarts the ESP32 when the first connection fails.
+void wifiBegin();
+
+bool wifiConnected();
+
+// Over-the-air updates of the ESP32 firmware (pio run -e esp32 -t upload)
+void otaBegin();
+void otaLoop();
+
+// After a crash or unexpected reset, run only OTA for OTA_PANIC_WINDOW, so a firmware that
+// crashes at boot can still be replaced. Does nothing after a normal power on.
+void otaPanicWindow(int led_pin);