feat: NTP time sync writing to DS3231 (by IP, DNS-independent)

This LAN's router does not resolve external hostnames, so NTP uses
hard-coded Cloudflare/Google anycast IPs instead of names.

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

WeatherPredictor/WeatherPredictor.ino

@@ -55,6 +55,10 @@ void setup() {
   displaySplash("WiFi", "Connect / portal");
   if (netBegin()) {
     Serial.printf("WiFi connected: %s\n", netIP().c_str());
+    if (ntpSync(settings.tzOffsetMin))
+      Serial.println(F("RTC synced from NTP"));
+    else
+      Serial.println(F("NTP sync failed"));
   } else {
     Serial.println(F("WiFi not connected - running offline"));
   }