feat: first-boot records what a server does with no settings

`gbrgames first-boot -game <id>` (or -image for a game with no template)
starts the server once like the node-agent does (same volumes, user,
SteamCMD install and startup prefix) but with none of the template's
settings and no restart policy, in the isolated gbr-boottest network.
It watches the console until the server exits, goes quiet or hits -max,
stops it gracefully (many servers write their settings on shutdown) and
records:
- the console with timings, plus ready and error lines; the last strong
  ready line before the stop becomes a readyPattern / readyExample pair
- every file created; config files are copied out and parsed into
  settings with their defaults (INI, properties, JSON, YAML, Unreal
  OptionSettings=(...) lists); log files are scanned for ready lines too
- files written outside the volumes, which a recreated container loses

Minecraft: ready line `Done \([0-9.]+s\)! For help, type "help"` and 76
settings (69 from server.properties) found with no template input. ARK:
showed its image retries nothing when SteamCMD fails with "Missing
configuration" and starts a server that was never installed.

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

.gitignore

@@ -4,3 +4,6 @@ export.json
 
 /gbrgames
 /gbrgames.exe
+
+# first-boot reports (logs and copied server files)
+firstboot-out/