Retire A2ML; install the repo deed (as trope-checker #98 / workbench #75) #82

Deferred from Phase 0 (PR #81); recorded, not done there.

What: this repo still carries the A2ML machine-readable tree (.machine_readable/, the *.a2ml manifests, machine-readable-design/ where present). trope-checker (833e85f, PR #98) and the workbench (63eb8bc, PR #75) have already retired theirs.

Recipe (from those two PRs):

1. Delete the .a2ml tree and machine-readable-design/.
2. Add haec_chora.deed — grammar: standards 1-formats/deed/spec/abnf/deed.abnf; record the clade decision in it.
3. Register the deed in root-allow.txt and coordination.k9.
4. Rewire the dogfood a2ml-validate job, pre-commit, Justfile, CODEOWNERS, dep5 and .gitattributes to the deed.

Needs: the deed validator. One PR for this repo alone. Deeds, root-allow.txt, coordination.k9 and .machine_readable/ are owner-only edits under the Phase 0 brief.