feat(display): boot icon carousel

On power-up, after the title splash the screen clears and each weather
icon slides in from the right to centre with its colour-coded label, then
slides out to the left — Fine, Fair, Changeable, Rain, Storm.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

WeatherPredictor/WeatherPredictor.ino

@@ -43,6 +43,8 @@ void setup() {
 
   displayBegin();
   displaySplash("Weather", "Predictor");
+  delay(800);
+  displayDemo();
 
   if (!sensorsBegin()) Serial.println(F("BMP180 not found!"));
   if (!rtcBegin())     Serial.println(F("DS3231 not found!"));

WeatherPredictor/display_ui.cpp

@@ -99,6 +99,46 @@ static void drawIcon(WxCategory c, int x, int y, int W, int H) {
 }
 
 // Layout for landscape 160 x 80.
+// Boot demo: each weather icon slides in from the right to centre, with its
+// category label below in the matching colour.
+void displayDemo() {
+  WxCategory cats[5]  = {WX_FINE, WX_FAIR, WX_CHANGEABLE, WX_RAIN, WX_STORM};
+  const char* names[5] = {"Fine", "Fair", "Changeable", "Rain", "Storm"};
+  const int W = 64, H = 52, y = 4;
+  const int cxc = (160 - W) / 2;          // centred icon x
+  tft.fillScreen(ST77XX_BLACK);           // clear the splash before the carousel
+  for (int k = 0; k < 5; k++) {
+    // slide in from the right edge to centre
+    int px = 160 + 12;
+    for (int x = 160; x >= cxc; x -= 12) {
+      tft.fillRect(px, y, W, H, ST77XX_BLACK);
+      drawIcon(cats[k], x, y, W, H);
+      px = x;
+      delay(26);
+    }
+    tft.fillRect(px, y, W, H, ST77XX_BLACK);
+    drawIcon(cats[k], cxc, y, W, H);
+    // label centred below in the category colour
+    int len = 0; while (names[k][len]) len++;        // size 2 = 12 px/char
+    tft.setTextSize(2);
+    tft.setTextColor(catColor(cats[k]));
+    tft.setCursor((160 - len * 12) / 2, 60);
+    tft.print(names[k]);
+    delay(360);
+    tft.fillRect(0, 60, 160, 20, ST77XX_BLACK);       // drop the label before it leaves
+    // slide out to the left edge
+    px = cxc;
+    for (int x = cxc - 12; x >= -W; x -= 12) {
+      tft.fillRect(px, y, W, H, ST77XX_BLACK);
+      drawIcon(cats[k], x, y, W, H);
+      px = x;
+      delay(24);
+    }
+    tft.fillRect(px, y, W, H, ST77XX_BLACK);           // clear the last remnant
+  }
+  tft.setTextColor(ST77XX_WHITE);
+}
+
 void displayRender(const AppState& s) {
   tft.fillScreen(ST77XX_BLACK);
   tft.setTextColor(ST77XX_WHITE);

WeatherPredictor/display_ui.h

@@ -4,4 +4,5 @@
 
 void displayBegin();
 void displaySplash(const char* line1, const char* line2);
+void displayDemo();                       // boot animation: icons slide in one by one
 void displayRender(const AppState& s);