ci: boot-test changed games before publishing

Only games whose folder changed are boot-tested (against the previous
main commit, or against main on branches; manual runs pick games). Each
one is deployed by the node-agent's real deploy code on a dedicated
game-test runner, in a network that can reach the internet but not the
LAN. Publishing to the panel runs only if they all booted.

- boottest-payload builds the DEPLOY_SERVER message the panel would send
- readyPattern/failPatterns in game.yaml; readyExample in test.yaml is
  checked against the pattern during validation
- secrets in test.yaml come from CI; a game missing one is skipped
- Minecraft gets a ready pattern; Dragonwilds needs DRAGONWILDS_OWNER_ID
- RUNNER.md + scripts/runner: runner, isolated network, systemd unit

Also fixes newline values ("\n" separators/footers) that yaml.v3 wrote
as "" on import, which would have broken ARK and Dragonwilds config
files once synced, and adds a round-trip test for the importer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/runner/gbr-boottest-network.service

@@ -0,0 +1,13 @@
+[Unit]
+Description=Isolated Docker network for GBR game boot tests
+After=docker.service
+Requires=docker.service
+PartOf=docker.service
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/opt/gbr-boottest/setup-boottest-network.sh
+
+[Install]
+WantedBy=docker.service