Establish MOUSE ports collection

Makefile

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+.PHONY: check
+
+check:
+	./tests/check-layout.sh

README.md

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+# MOUSE ports
+
+This repository is the independently versioned source-port collection for
+MOUSE. It contains third-party recipes and patches only; the `mouse-port`
+implementation, ports contract, base-system manifest, and release integration
+belong to `mouse-src`.
+
+Each port lives below `ports/NAME` and follows the recipe contract shipped by
+the compatible MOUSE base release. A MOUSE release pins one tested commit from
+this repository, while installed systems may move to later compatible ports
+revisions without replacing the base system.
+
+The adversarial and demonstration recipes used by the base-system acceptance
+suite are deliberately not part of this collection. They live in
+`mouse-src/tests/fixtures/ports`.
+
+Run the collection checks with:
+
+```sh
+make check
+```

infrastructure/README.md

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+# Infrastructure
+
+Collection-wide generation, lint, and publication tooling belongs here. Base
+image assembly and the `mouse-port` implementation remain in `mouse-src`.

ports/README.md

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+# Ports collection
+
+Each immediate child directory is one port named `[a-z][a-z0-9-]*` and contains
+one `port.conf` plus its trusted `build.sh` and any port-owned patches or files.
+
+The collection is intentionally empty until the first real third-party port is
+accepted. Test-only recipes do not belong here.

tests/check-layout.sh

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+#!/bin/sh
+set -eu
+
+root=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)
+found=0
+
+for directory in "$root"/ports/*; do
+	[ -d "$directory" ] || continue
+	[ "${directory##*/}" != README.md ] || continue
+	found=1
+	name=${directory##*/}
+	case "$name" in
+		""|[!a-z]*|*[!a-z0-9-]*)
+			printf '%s\n' "invalid port directory name: $name" >&2
+			exit 1
+			;;
+	esac
+	[ -f "$directory/port.conf" ] || {
+		printf '%s\n' "missing recipe: ports/$name/port.conf" >&2
+		exit 1
+	}
+	[ -x "$directory/build.sh" ] || {
+		printf '%s\n' "missing executable build script: ports/$name/build.sh" >&2
+		exit 1
+	}
+	sh -n "$directory/build.sh"
+done
+
+if [ "$found" -eq 0 ]; then
+	printf '%s\n' "ports collection is empty"
+else
+	printf '%s\n' "ports layout check passed"
+fi