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/flog.h

@@ -0,0 +1,16 @@
+#pragma once
+#include <Arduino.h>
+#include "forecast.h"
+
+struct FcastEntry {
+  uint32_t epoch;
+  char     letter;   // Zambretti 'A'..'Z'
+  uint8_t  cat;      // WxCategory
+};
+
+void       flogBegin();
+void       flogConsider(uint32_t epoch, const Forecast& f);  // logs only when it changes
+int        flogCount();
+FcastEntry flogGet(int i);   // 0 = oldest
+bool       flogSave();
+bool       flogLoad();