docs: publish Tend Compose continuity evidence

Export the reviewed allowlisted snapshot from private source commit 07c1655921f21ee5e4fc4d85639d199e8867b17d. This records the Docker Compose activation, schema-compatible rollback, and stateful migration resource findings from Observatory Preview 19 dogfooding.

AI-Assisted: OpenAI Codex
Signed-off-by: Cole Speelman <crspeelman@gmail.com>

scripts/test-public-snapshot.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-only
+set -euo pipefail
+root=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)
+work=$(mktemp -d)
+trap 'rm -rf -- "$work"' EXIT
+destination=$work/public
+"$root/scripts/export-public.sh" --destination "$destination" >/dev/null
+test -f "$destination/PUBLIC-SNAPSHOT.json"
+test -f "$destination/PUBLIC-SNAPSHOT.sha256"
+(cd "$destination" && sha256sum -c PUBLIC-SNAPSHOT.sha256)
+test ! -e "$destination/.git"
+test ! -e "$destination/.gitea"
+test ! -e "$destination/.github"
+while IFS= read -r file; do
+	cmp "$root/$file" "$destination/$file"
+done <"$root/scripts/public-snapshot.allow"
+echo "public snapshot isolation verified"