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/Makefile

@@ -0,0 +1,22 @@
+# Boxmaker gate. `make gate` must pass before any work is called done. It needs no network.
+
+.PHONY: gate audit verify-device
+
+gate:
+	cargo fmt --all --check
+	cargo clippy --workspace --all-targets --locked --offline -- -D warnings
+	cargo test --workspace --locked --offline
+	cargo deny --offline check bans licenses sources
+	sh scripts/check-lines.sh
+	sh scripts/check-crate-deps.sh
+	sh scripts/check-dep-docs.sh
+	sh scripts/test-gate-scripts.sh
+	@echo "gate: ok"
+
+# Fetches the RustSec advisory database. Listed in docs/egress.md.
+audit:
+	cargo deny check advisories
+
+# Checks that need straylight. Filled in from M2.
+verify-device:
+	@echo "verify-device: nothing to check until M2"