Add answer keys to workshops missing them

[beagandica]

Context

Based on a March 2026 audit of all 40 English workshops against our new WORKSHOP-STANDARDS.md, 14 workshops are missing answer-key.md files.

Answer keys should have hidden: true in the metadata block so they don't appear in student navigation.

Workshops missing answer keys (sorted by activity count)

Workshop	Activities	Priority
engdesign-distance	11	High
debugging	10	High
github-basics	10	High
machine-learning	10	High
csharp-basics	7	Medium
Kusto-KC7	7	Medium
java-datastructures	6	Medium
microbit-distance-checker	6	Medium
chatbot	5	Medium
ml-machine-learning	5	Medium
arduino	4	Lower
python-basics	4	Lower
adventure	2	Lower
microbit	1	Lower

Answer key template

---
title: "Answer Key"
draft: false
hidden: true
weight: 300
---