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>

docs/plans/M1/files/deny.toml

@@ -0,0 +1,25 @@
+# cargo-deny configuration. `make gate` runs bans, licenses and sources offline.
+# `make audit` runs advisories, which fetches the RustSec database.
+
+[graph]
+all-features = true
+
+[licenses]
+allow = ["MIT", "Apache-2.0", "Unicode-3.0"]
+confidence-threshold = 0.9
+
+[licenses.private]
+ignore = true
+
+[bans]
+multiple-versions = "deny"
+wildcards = "deny"
+allow-wildcard-paths = true
+
+[sources]
+unknown-registry = "deny"
+unknown-git = "deny"
+allow-registry = ["https://github.com/rust-lang/crates.io-index"]
+
+[advisories]
+yanked = "deny"