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/el512_display.h

@@ -5,6 +5,7 @@
 #include "cyberpunk.h"
 #include "el512_helpers.h"
 #include "konosuba.h"
+#include "steins.h"
 #include "el512_panel.h"
 #include "esphome/components/display/display_buffer.h"
 #include "esphome/core/component.h"