fix(builder): don't count Docker's init or the Steam client's own files as lost saves

Every container the node-agent starts gets /usr/sbin/docker-init, and SteamCMD
rewrites its own config.vdf on every run. Counted as files written outside the
volumes, they made every build look like it loses saves. A folder whose only
changes were logs no longer counts either, and a folder followed by a
same-named file (worlds, worlds.bak) is no longer taken for a file.

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

cmd/gbrgames/firstboot_test.go

@@ -113,15 +113,30 @@ A /home/steam/.config/example
 A /home/steam/.config/example/worlds
 A /home/steam/.config/example/worlds/world1.db
 A /home/steam/.config/example/worlds/world1.fwl
+A /home/steam/.config/example/worlds.bak
 A /home/steam/.config/example/Player.log
+C /home/steam/logs
+A /home/steam/logs/server.log
+C /home/steam/Steam
+C /home/steam/Steam/config
+C /home/steam/Steam/config/config.vdf
+C /home/steam/steamcmd/linux64/steamclient.so
 C /etc
 C /etc/hostname
+C /usr
+C /usr/sbin
+A /usr/sbin/docker-init
+C /var
+C /var/log
+A /var/log/x
 A /tmp/x.sock
 A /server/should-not-count.sav
 D /home/steam/old.txt
 A /home/steam/server.pid`
 	got := outsideFiles(diff, map[string]string{"/server": "v", "/data": "v"})
-	want := []string{"A /home/steam/.config/example/worlds/world1.db", "A /home/steam/.config/example/worlds/world1.fwl"}
+	// Folders whose only changes aren't the game's (logs, Docker's init) don't count either
+	want := []string{"A /home/steam/.config/example/worlds.bak", "A /home/steam/.config/example/worlds/world1.db",
+		"A /home/steam/.config/example/worlds/world1.fwl"}
 	if strings.Join(got, "|") != strings.Join(want, "|") {
 		t.Errorf("got %q\nwant %q", got, want)
 	}