teach: add Assets section for reusable lesson components

[cmonty14]

The teach skill has no guidance on shared lesson components. Every time an agent writes a new lesson it reinvents the stylesheet, the quiz widget, the copy button. By the third lesson the workspace has three slightly different versions of the same code.

This proposes adding an ## Assets section that introduces ./assets/ as the place for reusable components. The idea: read what's already there before writing something new, and write new reusable things as components rather than inlining them.

The section stays generic. I have my own opinionated defaults for style.css and copy.js that I did not include here because they're mine, not everyone's (specific dark theme hex values, exact clipboard button behavior). Those belong in a personal overlay, not upstream.

Note: the ./assets/* entry in the workspace file list was already present in the file, so this only adds the ## Assets section that the link points to.

The change is ready as a branch on my fork: https://github.com/cmonty14/skills/tree/teach/add-assets-section

Happy to adjust wording or placement if useful.

[Back2Basics]

You can use https://Conceptual.fyi/ MCP service. Conceptual already crawls concept based resources and puts it into a map of what needs to be learned before something else (prerequisites)