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_pages.h

@@ -2,6 +2,7 @@
 // Home Assistant values they show, and small drawing helpers.
 #pragma once
 
+#include <algorithm>
 #include <cctype>
 #include <cmath>
 #include <cstdarg>
@@ -10,6 +11,7 @@
 #include <string>
 
 #include "esphome/components/display/display.h"
+#include "esphome/core/time.h"
 
 namespace esphome::el512 {
 
@@ -30,7 +32,38 @@ struct HomeData {
   float house{NAN};        // W
   float grid{NAN};         // W, > 0 = import
   std::string agenda;      // sensor.el512_agenda events: "day|time|title;..."
+  std::string message;     // the panel's Message text
   Reading rooms[4];
+
+  // Today's solar power in 15-minute slots (highest value seen per slot; -1 =
+  // no data yet). Fed by record(), once a second from YAML.
+  static constexpr int SLOTS = 96;
+  float solar_slots[SLOTS];
+  int slots_day{-1};
+
+  HomeData() {
+    for (auto &s : this->solar_slots)
+      s = -1;
+  }
+  void record(ESPTime now) {
+    if (!now.is_valid())
+      return;
+    if (now.day_of_year != this->slots_day) {
+      this->slots_day = now.day_of_year;
+      for (auto &s : this->solar_slots)
+        s = -1;
+    }
+    float &slot = this->solar_slots[now.hour * 4 + now.minute / 15];
+    if (!std::isnan(this->solar))
+      slot = std::max(slot, this->solar);
+  }
+};
+
+// 1-bit sprite: rows of '#' (lit) and anything else (dark). Generated by the
+// tools/*_sprites.py files.
+struct Sprite {
+  uint8_t w, h;
+  const char *const *rows;
 };
 
 namespace fx {
@@ -68,5 +101,42 @@ inline int text_width(display::Display &it, display::BaseFont *font, const char
   return w;
 }
 
+// Draw a sprite (optionally only its first `rows` rows), scaled up in blocks.
+inline void sprite(display::Display &it, const Sprite &s, int x, int y, int scale = 1, int rows = -1,
+                   Color color = display::COLOR_ON) {
+  const int h = rows < 0 ? s.h : std::min<int>(rows, s.h);
+  for (int r = 0; r < h; r++) {
+    for (int c = 0; c < s.w; c++) {
+      if (s.rows[r][c] != '#')
+        continue;
+      if (scale == 1)
+        it.draw_pixel_at(x + c, y + r, color);
+      else
+        it.filled_rectangle(x + c * scale, y + r * scale, scale, scale, color);
+    }
+  }
+}
+
+// Point on a circle; angle in degrees, 0 = up, clockwise.
+inline void polar(int cx, int cy, float r, float a, int *x, int *y) {
+  constexpr float DEG = 3.14159265f / 180.0f;
+  *x = cx + (int) std::lround(r * std::sin(a * DEG));
+  *y = cy - (int) std::lround(r * std::cos(a * DEG));
+}
+
+// Circular arc from angle a0 to a1 (degrees, as polar()).
+inline void arc(display::Display &it, int cx, int cy, float r, float a0, float a1) {
+  const int steps = std::max(2, (int) (std::fabs(a1 - a0) / 5));
+  int px, py;
+  polar(cx, cy, r, a0, &px, &py);
+  for (int i = 1; i <= steps; i++) {
+    int nx, ny;
+    polar(cx, cy, r, a0 + (a1 - a0) * i / steps, &nx, &ny);
+    it.line(px, py, nx, ny);
+    px = nx;
+    py = ny;
+  }
+}
+
 }  // namespace fx
 }  // namespace esphome::el512