feat: let teach skill share code between lessons via ./assets

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.changeset/teach-shared-assets.md

@@ -0,0 +1,5 @@
+---
+"mattpocock-skills": patch
+---
+
+Allow the **`teach`** skill to share code between lessons. Shared stylesheets, simulator code, and any code reused across lessons now live in `./assets/`.

skills/productivity/teach/SKILL.md

@@ -16,6 +16,7 @@ Treat the current directory as a teaching workspace. The state of their learning
 - `RESOURCES.md`: A list of resources which can be explored to ground your teaching in contextual knowledge, or to acquire knowledge and wisdom. Use the format in [RESOURCES-FORMAT.md](./RESOURCES-FORMAT.md).
 - `./learning-records/*.md`: A directory of learning records, which capture what the user has learned. These are loosely equivalent to architectural decision records in software development - they capture non-obvious lessons and key insights that may need to be revised later, or drive future sessions. These should be used to calculate the zone of proximal development. They are titled `0001-<dash-case-name>.md`, where the number increments each time. Use the format in [LEARNING-RECORD-FORMAT.md](./LEARNING-RECORD-FORMAT.md).
 - `./lessons/*.html`: A directory of lessons. A **lesson** is a single, self-contained HTML output that teaches one tightly-scoped thing tied to the mission. This is the primary unit of teaching in this workspace.
+- `./assets/*`: Shared code used across lessons — stylesheets, simulator code, anything two or more lessons reuse. Lessons may link to these rather than duplicating the code inline.
 - `NOTES.md`: A scratchpad for you to jot down user preferences, or working notes.
 
 ## Philosophy