Add M1 plan, given tests and fixtures, AGENTS.md and implementer log

Seven task files for the implementing model under docs/plans/M1/, with
the test files, byte-exact fixtures, Makefile, deny.toml and gate-script
self-test they copy into place. All of it was verified against a private
reference implementation: the gate passes after every task in order.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,3 @@
 /target/
 /spike/out/
+/.state/