Add four animated KonoSuba ESPHome pages

Megumin's daily explosion, the Adventurers' Guild quest board (agenda,
weather, solar), Megumin's adventurer card and a party battle against a
giant toad with a live-data battle log. Original 1-bit pixel art lives in
tools/konosuba_sprites.py, which generates konosuba_sprites.h and can
render a preview PNG.

Home data and drawing helpers shared by the themed pages move to
el512_pages.h; the display gains dither_mask() for a dissolve-in intro.

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

components/el512/el512_display.cpp

@@ -148,6 +148,24 @@ void EL512Display::invert_rect(int x, int y, int width, int height) {
       this->panel_->setPixel(px, py, !this->panel_->getPixel(px, py));
 }
 
+void EL512Display::dither_mask(int level) {
+  if (this->panel_ == nullptr || level >= 16)
+    return;
+  static const uint8_t BAYER[4][4] = {{0, 8, 2, 10}, {12, 4, 14, 6}, {3, 11, 1, 9}, {15, 7, 13, 5}};
+  uint8_t masks[4];
+  for (int r = 0; r < 4; r++) {
+    masks[r] = 0;
+    for (int x = 0; x < 8; x++)
+      if (BAYER[r][x & 3] < level)
+        masks[r] |= 0x80 >> x;
+  }
+  uint8_t *fb = this->panel_->framebuffer();
+  constexpr int ROW = EL512Panel::WIDTH / 8;
+  for (int y = 0; y < EL512Panel::HEIGHT; y++)
+    for (int i = 0; i < ROW; i++)
+      fb[y * ROW + i] &= masks[y & 3];
+}
+
 void EL512Display::update() {
   if (this->panel_ == nullptr || !this->panel_->running())
     return;