Scaffold Exercises

This scaffolds exercise directory structures for what looks like an AI Hero course repository, creating the section and exercise folders with the right numeric prefixes, generating stub readme files, and running a linter to make sure everything's valid before you commit. It handles the three exercise variants (problem, solution, explainer) and knows all the lint rules like non-empty readmes, no broken links, and when you need a main.ts file. The workflow is parse your plan, mkdir everything, stub out readmes with titles, lint, fix, repeat. Saves you from manually creating dozens of folders and forgetting which exercises need which variants, then discovering lint failures after the fact.