feat: persist pressure history to LittleFS across reboots

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

WeatherPredictor/history.h

@@ -13,3 +13,5 @@ int    historyCount();
 Sample historyGet(int i);      // 0 = oldest
 Sample historyLatest();
 bool   historyTrendDelta(float& outDeltaHpa);
+bool   historySave();
+bool   historyLoad();