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!"));