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/system/settings_store.cpp

@@ -0,0 +1,40 @@
+#include "system/settings_store.h"
+
+#include <Preferences.h>
+
+static const char *NAMESPACE = "flipdot";
+static const char *KEY = "settings";
+// Increase when the Settings struct changes; old records are then ignored (defaults)
+static const uint16_t VERSION = 1;
+
+struct StoredSettings
+{
+	uint16_t version;
+	uint16_t size;
+	Settings settings;
+};
+
+void loadSettings(Settings &settings)
+{
+	settings = Settings();
+	StoredSettings stored;
+	Preferences prefs;
+	prefs.begin(NAMESPACE, true);
+	size_t read = prefs.getBytes(KEY, &stored, sizeof(stored));
+	prefs.end();
+	if (read == sizeof(stored) && stored.version == VERSION && stored.size == sizeof(Settings) &&
+		validateSettings(stored.settings) == nullptr)
+		settings = stored.settings;
+}
+
+void saveSettings(const Settings &settings)
+{
+	StoredSettings stored;
+	stored.version = VERSION;
+	stored.size = sizeof(Settings);
+	stored.settings = settings;
+	Preferences prefs;
+	prefs.begin(NAMESPACE, false);
+	prefs.putBytes(KEY, &stored, sizeof(stored));
+	prefs.end();
+}

src/esp32/system/settings_store.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include "logic/settings.h"
+
+// The web UI settings in NVS. A missing or outdated record gives the defaults.
+void loadSettings(Settings &settings);
+void saveSettings(const Settings &settings);