Icons: small images of their own size for pages

Bitmaps that only pages use (backgrounds, images by state) are now icons:
own width and height, stored in /icons, not in the page lists or the Home
Assistant dropdowns. Page backgrounds and image elements use icons or
bitmaps; the renderer gets icons expanded at the top left, so pages look
the same. Web UI: Icons tab with an editor, Make icon / Make bitmap, Save
as icon on the Draw tab, icons in the backup.

A one-time migration in time-boxed steps moves the uploaded bitmaps that
only pages use, after the new firmware is marked good.

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

src/esp32/system/firmware_guard.cpp

@@ -138,6 +138,11 @@ void firmwareGuardStopWatchdog()
 	watchdog_running = false;
 }
 
+bool firmwareGuardPending()
+{
+	return firmware_pending;
+}
+
 void firmwareGuardLoop(bool wifi_connected)
 {
 	if (watchdog_running)