test: pin the external fixtures and run the suites against the silo binary

The test and verification scripts invoked ./minio and pulled their tooling from
upstream infrastructure with no integrity check. Every `curl | tar` of a client
or an old server binary was an unverified execution path in a script that
regularly runs as a privileged user, and several fetched a floating "latest".

Two installers replace all of it:

- install-mcli.sh resolves a pinned pgsty/mc release, downloads the archive and
  its checksum manifest, requires exactly one valid manifest entry for the
  asset, verifies it, and installs. MCLI_BIN with a mandatory MCLI_SHA256 lets
  an offline or air-gapped run supply its own binary, still checksum-checked.
- install-verified-fixture.sh takes source, expected SHA-256 and target, and
  refuses anything that does not match. Sources may be a URL or a local file.

Every script that previously downloaded mc now calls install-mcli.sh. The three
places that genuinely need an upstream artifact - the old MinIO server binary
for the LDAP IAM upgrade-import test, the 2021 mc for the three-site
replication test, and the functional-tests.sh fixture - go through
install-verified-fixture.sh with the digest recorded inline. Those dl.min.io
URLs remain on purpose: they are historical upstream artifacts needed to prove
upgrade compatibility, and they are now pinned and verified rather than
trusted.

The scripts otherwise switch to ./silo, silo.service, the silo container and
compose service names, and SILO_CONFIG_DIR. run-multi-site-minio-idp.sh is
renamed to run-multi-site-silo-idp.sh with the Makefile target following.
buildscripts/minio-upgrade.sh keeps its name and its `minio server` argv - it
exists to test the MinIO-to-Silo upgrade, so the old side must stay old - but
it is now pinned to an image digest rather than a tag, and its `docker system
prune` and `docker volume prune` calls are removed. Those ran unfiltered
against the developer's whole Docker installation; the resiliency tests had the
same problem and lose their prune and `docker ps -q` sweeps too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

buildscripts/install-mcli.sh

@@ -0,0 +1,91 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [ "$#" -ne 1 ]; then
+	echo "usage: $0 TARGET" >&2
+	exit 2
+fi
+
+target=$1
+target_dir=$(dirname "${target}")
+if [ ! -d "${target_dir}" ]; then
+	echo "target directory does not exist: ${target_dir}" >&2
+	exit 1
+fi
+
+sha256_file() {
+	if command -v sha256sum >/dev/null 2>&1; then
+		sha256sum "$1" | awk '{print $1}'
+	else
+		shasum -a 256 "$1" | awk '{print $1}'
+	fi
+}
+
+if [ -n "${MCLI_BIN:-}" ]; then
+	if [ ! -f "${MCLI_BIN}" ]; then
+		echo "MCLI_BIN is not a regular file: ${MCLI_BIN}" >&2
+		exit 1
+	fi
+	if ! printf '%s\n' "${MCLI_SHA256:-}" | grep -Eq '^[0-9a-fA-F]{64}$'; then
+		echo "MCLI_SHA256 must contain the expected SHA-256 for MCLI_BIN" >&2
+		exit 1
+	fi
+	actual=$(sha256_file "${MCLI_BIN}")
+	if [ "${actual}" != "${MCLI_SHA256,,}" ]; then
+		echo "MCLI_BIN checksum mismatch: expected ${MCLI_SHA256,,}, got ${actual}" >&2
+		exit 1
+	fi
+	install -m 0755 "${MCLI_BIN}" "${target}"
+	exit 0
+fi
+
+release=${MCLI_RELEASE:-RELEASE.2026-08-04T00-00-00Z}
+version_hyphen=${release#RELEASE.}
+package_version=$(printf '%s\n' "${version_hyphen}" | sed -E 's/^([0-9]{4})-([0-9]{2})-([0-9]{2})T([0-9]{2})-([0-9]{2})-([0-9]{2})Z$/\1\2\3\4\5\6.0.0/')
+if [ "${package_version}" = "${version_hyphen}" ]; then
+	echo "invalid MCLI_RELEASE: ${release}" >&2
+	exit 1
+fi
+
+case $(uname -s) in
+	Linux) os=linux ;;
+	Darwin) os=darwin ;;
+	*) echo "unsupported mcli host OS: $(uname -s)" >&2; exit 1 ;;
+esac
+case $(uname -m) in
+	x86_64 | amd64) arch=amd64 ;;
+	aarch64 | arm64) arch=arm64 ;;
+	*) echo "unsupported mcli host architecture: $(uname -m)" >&2; exit 1 ;;
+esac
+
+archive="mcli_${package_version}_${os}_${arch}.tar.gz"
+checksums="mcli_${package_version}_checksums.txt"
+base_url="https://github.com/pgsty/mc/releases/download/${release}"
+tmp_dir=$(mktemp -d "${TMPDIR:-/tmp}/silo-mcli.XXXXXX")
+trap 'rm -rf "${tmp_dir}"' EXIT
+
+curl --fail --location --retry 3 --silent --show-error \
+	"${base_url}/${checksums}" --output "${tmp_dir}/${checksums}"
+curl --fail --location --retry 3 --silent --show-error \
+	"${base_url}/${archive}" --output "${tmp_dir}/${archive}"
+
+expected=$(awk -v asset="${archive}" '
+	{
+		name=$2
+		sub(/^\*/, "", name)
+		if (name == asset && $1 ~ /^[0-9a-fA-F]{64}$/) print tolower($1)
+	}
+' "${tmp_dir}/${checksums}")
+if ! printf '%s\n' "${expected}" | grep -Eq '^[0-9a-f]{64}$'; then
+	echo "checksum manifest does not contain exactly one valid entry for ${archive}" >&2
+	exit 1
+fi
+actual=$(sha256_file "${tmp_dir}/${archive}")
+if [ "${actual}" != "${expected}" ]; then
+	echo "downloaded ${archive} checksum mismatch" >&2
+	exit 1
+fi
+
+tar -xzf "${tmp_dir}/${archive}" -C "${tmp_dir}" mcli
+install -m 0755 "${tmp_dir}/mcli" "${target}"