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/web_server.h

@@ -0,0 +1,3 @@
+#pragma once
+void webBegin();
+void webLoop();