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/net.h

@@ -0,0 +1,6 @@
+#pragma once
+#include <Arduino.h>
+
+bool   netBegin();
+bool   netConnected();
+String netIP();