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/app.cpp

@@ -0,0 +1,122 @@
+#include "app.h"
+
+#include <string.h>
+
+#include "config.h"
+#include "display/bitmap_store.h"
+#include "system/settings_store.h"
+
+NanoLink nano(Serial2, NANO_RX_PIN, NANO_TX_PIN, RELAY_PIN, NANO_RESET_PIN);
+BROSE9323 display(DISPLAY_WIDTH, DISPLAY_HEIGHT, PANEL_WIDTH);
+FlipdotFrames frames(display);
+StatusScreen status(display, nano);
+DisplayController controller(nano, frames);
+
+static Settings settings;
+static bool restart_pending = false;
+static uint32_t restart_at = 0;
+
+// Load the page bitmap into the frames; falls back to the clock when it is gone
+static void applyPage()
+{
+	if (strcmp(settings.page, PAGE_CLOCK) != 0)
+	{
+		uint8_t bitmap[BITMAP_BYTES];
+		if (loadBitmap(settings.page, bitmap))
+		{
+			frames.setPageBitmap(bitmap);
+			controller.setPage(Page::Bitmap);
+			return;
+		}
+		Serial.printf("Page bitmap \"%s\" not found, showing the clock\n", settings.page);
+	}
+	controller.setPage(Page::Clock);
+}
+
+static void apply()
+{
+	controller.setSettings(settings.schedule, settings.clock);
+	status.setFlipTime(settings.flip_time);
+	applyPage();
+}
+
+const Settings &appSettings()
+{
+	return settings;
+}
+
+void appLoadSettings()
+{
+	loadSettings(settings);
+	apply();
+}
+
+static bool sameHomeAssistant(const HomeAssistantSettings &a, const HomeAssistantSettings &b)
+{
+	return a.enabled == b.enabled && a.port == b.port && strcmp(a.host, b.host) == 0 &&
+		   strcmp(a.user, b.user) == 0 && strcmp(a.password, b.password) == 0;
+}
+
+const char *appSaveSettings(const Settings &new_settings, bool &restart_needed)
+{
+	const char *error = validateSettings(new_settings);
+	if (error)
+		return error;
+	if (strcmp(new_settings.page, PAGE_CLOCK) != 0 && !bitmapExists(new_settings.page))
+		return "Bitmap not found";
+
+	restart_needed = !sameHomeAssistant(settings.home_assistant, new_settings.home_assistant);
+	bool flip_time_changed = settings.flip_time != new_settings.flip_time;
+	settings = new_settings;
+	saveSettings(settings);
+	apply();
+	if (flip_time_changed && nano.isOn())
+		display.setTiming(settings.flip_time);
+	return nullptr;
+}
+
+const char *appSelectPage(const char *name)
+{
+	if (strcmp(name, PAGE_CLOCK) != 0 && !bitmapExists(name))
+		return "Bitmap not found";
+	strncpy(settings.page, name, sizeof(settings.page) - 1);
+	settings.page[sizeof(settings.page) - 1] = '\0';
+	saveSettings(settings);
+	applyPage();
+	return nullptr;
+}
+
+void appBitmapChanged(const char *name)
+{
+	if (strcmp(settings.page, name) == 0)
+	{
+		applyPage();
+		controller.pageChanged();
+	}
+}
+
+void appShowLive(const uint8_t *bitmap)
+{
+	frames.setLiveBitmap(bitmap);
+	controller.showLive(millis());
+}
+
+void appStopLive()
+{
+	controller.stopLive();
+}
+
+void appRestartLater(uint32_t delay_ms)
+{
+	restart_pending = true;
+	restart_at = millis() + delay_ms;
+}
+
+void appLoop()
+{
+	if (restart_pending && (int32_t)(millis() - restart_at) >= 0)
+	{
+		Serial.println("Restarting for the new settings");
+		ESP.restart();
+	}
+}