chore: make repo an Arduino collection with WeatherPredictor project

Flatten so the repo root is the Arduino sketchbook; the project lives in
WeatherPredictor/. Add a collection index README at the root and move the
detailed project README into WeatherPredictor/.

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

WeatherPredictor/rtc_time.cpp

@@ -0,0 +1,42 @@
+#include <RTClib.h>
+#include <time.h>
+#include <ESP8266WiFi.h>
+#include "config.h"
+#include "rtc_time.h"
+
+static RTC_DS3231 rtc;
+
+bool rtcBegin()      { return rtc.begin(); }
+bool rtcLostPower()  { return rtc.lostPower(); }
+
+RtcTime rtcNow() {
+  DateTime n = rtc.now();
+  return RtcTime{ n.year(), n.month(), n.day(), n.hour(), n.minute(), n.second() };
+}
+
+void rtcSet(const RtcTime& t) {
+  rtc.adjust(DateTime(t.year, t.month, t.day, t.hour, t.minute, t.second));
+}
+
+uint32_t rtcEpoch() {
+  return rtc.now().unixtime();
+}
+
+bool ntpSync(int tzOffsetMin) {
+  // NTP servers by IP to bypass DNS (this network doesn't resolve names reliably).
+  // Cloudflare (162.159.200.123) and Google (216.239.35.0/.4) are stable anycast.
+  configTime(tzOffsetMin * 60, 0, "162.159.200.123", "216.239.35.0", "216.239.35.4");
+  time_t now = time(nullptr);
+  int tries = 0;
+  while (now < 1700000000 && tries < 120) {        // up to ~30 s
+    delay(250);
+    now = time(nullptr);
+    tries++;
+  }
+  if (now < 1700000000) return false;
+  struct tm* lt = localtime(&now);
+  rtcSet(RtcTime{ (uint16_t)(lt->tm_year + 1900), (uint8_t)(lt->tm_mon + 1),
+                  (uint8_t)lt->tm_mday, (uint8_t)lt->tm_hour,
+                  (uint8_t)lt->tm_min, (uint8_t)lt->tm_sec });
+  return true;
+}