Add four Steins;Gate pages; shuffle the page rotation hourly

Divergence meter (Nixie tubes, world lines and clock), a D-mail sent
through the Phone Microwave using the panel's Message text, the Future
Gadget Lab inventory with live sensors, and a world line chart of today's
solar power. Original pixel art in tools/steins_sprites.py; the sprite
tool is shared between themes and Sprite, sprite(), polar() and arc()
move to el512_pages.h. HomeData gains the message and a 24 h solar
history in 15-minute slots.

The rotation now walks all pages in a random order that is reshuffled
every hour (Still Alive stays out, Now playing is skipped when idle).

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

components/el512/konosuba_sprites.h

@@ -2,15 +2,10 @@
 // edit the art there. Original 1-bit fan art, '#' = lit pixel.
 #pragma once
 
-#include <stdint.h>
+#include "el512_pages.h"  // Sprite
 
 namespace esphome::el512::konosuba {
 
-struct Sprite {
-  uint8_t w, h;
-  const char *const *rows;
-};
-
 static const char *const MEGUMIN_ROWS[] = {
     "...............####.........",
     "..............######........",