Add a web UI to the clock firmware

- Web UI on port 80: live view of the display, choose the page (clock or
  a bitmap), bitmaps (list, show, live, edit, delete), draw / image upload
  with conversion in the browser, live mode, settings, Home Assistant
- Live view from a shadow buffer in the BROSE9323 driver (shownPixel)
- Settings in NVS with the original behaviour as defaults: schedule times,
  quarter hours, yawning Pikachu, No WiFi screen, flip time, status LED,
  Home Assistant broker (restart on change)
- Bitmaps on LittleFS; new 320 KB partition, ota slots now 1.31 MB
- DisplayController: pages, live mode, settings; app.cpp holds the objects
- README for the recovery app; docs for the web UI
- Tests: settings, time parsing, bitmap format and names, schedule with
  settings, pages and live mode (95 total)

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

src/esp32/net/home_assistant.cpp

@@ -22,6 +22,7 @@ static char firmware_status[64] = "";
 static bool firmware_status_sent = false;
 
 static DisplayController *displayController = nullptr;
+static bool enabled = false;
 
 // The switches are not optimistic: the new state must be reported back to Home Assistant
 static void onClockCommand(bool state, HASwitch *sender)
@@ -36,9 +37,15 @@ static void onPowerCommand(bool state, HASwitch *sender)
 	sender->setState(state);
 }
 
-void homeAssistantBegin(DisplayController &controller)
+void homeAssistantBegin(DisplayController &controller, const HomeAssistantSettings &settings)
 {
 	displayController = &controller;
+	enabled = settings.enabled;
+	if (!enabled)
+	{
+		Serial.println("Home Assistant disabled in the settings");
+		return;
+	}
 
 	device.setName(HA_DEVICE_NAME);
 	device.setSoftwareVersion(HA_SOFTWARE_VERSION);
@@ -62,11 +69,23 @@ void homeAssistantBegin(DisplayController &controller)
 	// The sensor doesn't resend its value on reconnect by itself
 	mqtt.onConnected([]() { firmware_status_sent = false; });
 
-	mqtt.begin(BROKER_ADDR, MQTT_USER, MQTT_PASSWORD);
+	// settings must stay alive: the MQTT library keeps the pointers
+	if (settings.host[0])
+		mqtt.begin(settings.host, settings.port, settings.user[0] ? settings.user : nullptr,
+				   settings.password[0] ? settings.password : nullptr);
+	else
+		mqtt.begin(BROKER_ADDR, settings.port, MQTT_USER, MQTT_PASSWORD); // secrets.h
+}
+
+bool homeAssistantConnected()
+{
+	return enabled && mqtt.isConnected();
 }
 
 void homeAssistantLoop()
 {
+	if (!enabled)
+		return;
 	mqtt.loop();
 	if (!firmware_status_sent && firmware_status[0] && mqtt.isConnected())
 		firmware_status_sent = firmwareSensor.setValue(firmware_status);