Add dynamic pages with clock, date, Home Assistant values and fonts

The hardcoded clock is now the built-in dynamic page "Clock". A dynamic page
has a background bitmap per time of day and up to 8 elements (clock, date,
Home Assistant value, text), each with position, alignment, font and overlay.
Pages are drawn on the ESP32, also for the web previews.

- Pages tab in the web UI: page editor with drag and drop, font upload
  (TTF/OTF converted in the browser to the FDF1 dot font format)
- Built-in fonts Small, Normal, Large and Full height (generated by
  tools/make_builtin_fonts.py), built-in bitmaps Pikachu and Pikachu yawning
- Home Assistant values over the REST API (URL and token in the HA tab)
- Settings version 4: evening settings removed (now time slots of the Clock
  page), old records are converted
- HA Mode dropdown lists the dynamic pages and bitmaps

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

src/esp32/system/settings_store.cpp

@@ -7,21 +7,77 @@
 static const char *NAMESPACE = "flipdot";
 static const char *KEY = "settings";
 // Increase when the Settings struct changes; old records are then ignored (defaults),
-// unless OLD_VERSIONS says how to read them
-static const uint16_t VERSION = 3;
+// unless the code below says how to read them. When fields are only added at the end,
+// an old record is the start of the new layout: add an OldVersion for it like v3 does.
+static const uint16_t VERSION = 4;
 
-// Older versions: fields were only added at the end, so the start of an old record has
-// the same layout. New fields keep their defaults.
 struct OldVersion
 {
 	uint16_t version;
-	size_t fields; // bytes of Settings that version had
+	size_t fields; // bytes of the settings struct that version had
 };
-static const OldVersion OLD_VERSIONS[] = {
+
+// Versions 1-3: the layout before the dynamic pages (version 4 removed the evening
+// settings of the clock and added the Home Assistant API). Frozen copy, read as a prefix
+// (version 1 lacked off_page and drive, version 2 drive) and converted.
+namespace v3
+{
+struct ClockSettings
+{
+	bool evening_enabled = true;
+	uint16_t evening_start = 17 * 60;
+	bool no_wifi_screen = true;
+};
+
+struct HomeAssistantSettings
+{
+	bool enabled = true;
+	char host[64] = "";
+	uint16_t port = 1883;
+	char user[32] = "";
+	char password[64] = "";
+};
+
+struct Settings
+{
+	char page[25] = "clock";
+	ScheduleSettings schedule;
+	ClockSettings clock;
+	HomeAssistantSettings home_assistant;
+	uint16_t flip_time = 225;
+	bool status_led = true;
+	char off_page[25] = "";
+	DriveSettings drive;
+};
+
+static const OldVersion VERSIONS[] = {
 	{1, offsetof(Settings, off_page)},
 	{2, offsetof(Settings, drive)},
+	{3, sizeof(Settings)},
 };
 
+static void convert(const Settings &old, ::Settings &s)
+{
+	s = ::Settings();
+	memcpy(s.page, old.page, sizeof(s.page));
+	s.schedule = old.schedule;
+	s.clock.no_wifi_screen = old.clock.no_wifi_screen;
+	const HomeAssistantSettings &ha = old.home_assistant;
+	s.home_assistant.enabled = ha.enabled;
+	memcpy(s.home_assistant.host, ha.host, sizeof(ha.host));
+	s.home_assistant.port = ha.port;
+	memcpy(s.home_assistant.user, ha.user, sizeof(ha.user));
+	memcpy(s.home_assistant.password, ha.password, sizeof(ha.password));
+	s.flip_time = old.flip_time;
+	s.status_led = old.status_led;
+	memcpy(s.off_page, old.off_page, sizeof(s.off_page));
+	s.drive = old.drive;
+	// The evening (yawning Pikachu from 17:00) is now a time slot of the built-in Clock page
+}
+} // namespace v3
+
+static_assert(sizeof(v3::Settings) <= sizeof(Settings), "the old record must fit the buffer");
+
 struct StoredSettings
 {
 	uint16_t version;
@@ -29,6 +85,16 @@ struct StoredSettings
 	Settings settings;
 };
 
+// Reads a record whose first `fields` bytes have the layout of T
+template <typename T> static bool readOld(const StoredSettings &stored, size_t read, size_t fields, T &out)
+{
+	if (stored.size < fields || stored.size > sizeof(T) || read != offsetof(StoredSettings, settings) + stored.size)
+		return false;
+	out = T();
+	memcpy((void *)&out, &stored.settings, fields);
+	return true;
+}
+
 void loadSettings(Settings &settings)
 {
 	settings = Settings();
@@ -44,14 +110,17 @@ void loadSettings(Settings &settings)
 		loaded = stored.settings;
 	else
 	{
-		const OldVersion *old = nullptr;
-		for (const OldVersion &o : OLD_VERSIONS)
+		bool ok = false;
+		for (const OldVersion &o : v3::VERSIONS)
 			if (o.version == stored.version)
-				old = &o;
-		if (!old || stored.size < old->fields || stored.size > sizeof(Settings) ||
-			read != offsetof(StoredSettings, settings) + stored.size)
+			{
+				v3::Settings old;
+				ok = readOld(stored, read, o.fields, old);
+				if (ok)
+					v3::convert(old, loaded);
+			}
+		if (!ok)
 			return;
-		memcpy((void *)&loaded, &stored.settings, old->fields);
 	}
 	if (validateSettings(loaded) == nullptr)
 		settings = loaded;