Clarify that optional bullets become substantive grouped lists when the diff
is large or spans several concerns.
- Adjust the workflow-rules bullet that describes Conventional Commit bodies.
Introduce root-level AGENTS.md as the architecture and workflow summary for
humans and coding agents. Add docs/src/repository_layout.md as a placement
and anti-pattern reference for sources, tests, scripts, and gitignored trees.
- AGENTS.md links deep docs and states 2.0 invariants
- repository_layout.md includes .cursor/ as gitignored local tooling