feat: persistent settings in LittleFS JSON

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

WeatherPredictor/WeatherPredictor.ino

@@ -6,6 +6,7 @@
 #include "rtc_time.h"
 #include "forecast.h"
 #include "history.h"
+#include "app_settings.h"
 
 static void i2cScan() {
   Serial.println(F("I2C scan:"));
@@ -59,6 +60,14 @@ void setup() {
                   historyCount(), d, classifyTrend(d));
   else
     Serial.println(F("history: not enough data for trend"));
+
+  // --- settings self-test (remove after Task 8) ---
+  settingsBegin();
+  Serial.printf("settings: alt=%.0f tz=%d lat=%.4f lon=%.4f\n",
+                settings.altitudeM, settings.tzOffsetMin, settings.lat, settings.lon);
+  settings.altitudeM += 1.0f;   // change and persist to test round-trip
+  settingsSave();
+  Serial.println(F("settings: incremented altitude and saved"));
 }
 
 void loop() {