Add automated checks for lesson pin-map consistency #5

The lesson tables and sketches currently duplicate pin assignments. Add a lightweight validation tool that detects drift without introducing a runtime dependency for students.

Acceptance criteria

• define a machine-readable pin map or reliably parse named constants
• verify each lesson's documented pins against its matching sketch
• run the check in CI
• produce an actionable error naming the lesson, signal, expected pin, and actual pin
• document how contributors update a pin map

Keep the .ino files directly openable in Arduino IDE and easy for beginners to read.