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/display/page_resources.cpp

@@ -4,6 +4,7 @@
 
 #include "display/bitmap_store.h"
 #include "display/font_store.h"
+#include "display/icon_store.h"
 #include "net/ha_api.h"
 
 Stopwatch stopwatch;
@@ -11,7 +12,13 @@ StoredPageResources pageResources(stopwatch);
 
 bool StoredPageResources::background(const char *name, uint8_t *bitmap)
 {
-	return loadBitmap(name, bitmap);
+	if (loadBitmap(name, bitmap))
+		return true;
+	Icon icon;
+	if (!loadIcon(name, icon))
+		return false;
+	iconToBitmap(icon, bitmap); // at the top left: images are drawn from their x, y
+	return true;
 }
 
 Font StoredPageResources::font(const char *name)