Create cheat sheets for each concept doc

[travisjneuman]

Description

Create single-page cheat sheets (PDF or Markdown) summarizing the key points from each concept doc. Learners can print these or keep them open while coding.

Scope

• Create a concepts/cheatsheets/ directory
• Start with the 7 beginner concept docs
• Each cheat sheet should fit on one page when printed

Acceptance Criteria

• At least 7 cheat sheets (one per beginner concept)
• Each cheat sheet has: key syntax, common patterns, common mistakes, quick reference
• Markdown format with clean formatting that renders well on GitHub
• A README in the cheatsheets directory linking to all sheets

[travisjneuman]

Resolved in 36dceb1: Created 8 cheat sheets at concepts/cheatsheets/ covering variables, types, strings, loops, functions, collections, files, and errors. Includes README index.