docs: rewrite course authoring guide as procedural LLM-facing instructions

.changeset/agents-procedural-rewrite.md

@@ -0,0 +1,5 @@
+---
+'tessera-learn': patch
+---
+
+Rewrite the course authoring guide (`AGENTS.md`) into a procedural, LLM-facing instruction set — converting prose to rules/tables and trimming runtime-internal reference that authors never write.

CONTRIBUTING.md

@@ -35,7 +35,7 @@ AGENTS.md            # Monorepo dev guide (working on Tessera itself)
 
 ## Editing the authoring guide
 
-The course authoring guide lives at `packages/tessera-learn/AGENTS.md`. Edit it there — it ships in `tessera-learn`'s `files` field, so it installs into every scaffolded project at `node_modules/tessera-learn/AGENTS.md`. There is no copy of it elsewhere: `create-tessera` scaffolds only small pointer stubs (`packages/create-tessera/templates/base/CLAUDE.md` imports the guide for Claude Code; `…/AGENTS.md` points other agents at it). The repo-root `AGENTS.md` is a separate document: the monorepo dev guide for working on Tessera itself.
+The course authoring guide lives at `packages/tessera-learn/AGENTS.md`. Edit it there — it ships in `tessera-learn`'s `files` field, so it installs into every scaffolded project at `node_modules/tessera-learn/AGENTS.md`. There is no copy of it elsewhere: `create-tessera` scaffolds only a small pointer stub from `packages/create-tessera/templates/workspace/AGENTS.md`, which `@`-imports the guide and is copied to both `AGENTS.md` and `CLAUDE.md` at the workspace root so every agent finds one. The repo-root `AGENTS.md` is a separate document: the monorepo dev guide for working on Tessera itself.
 
 ## Branch + commit style