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>

cmd/gbrgames/firstboot_test.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"regexp"
+	"testing"
+)
+
+func TestParseConfigFormats(t *testing.T) {
+	// Palworld's Unreal-style list
+	pal := parseConfig("/server/Pal/Saved/Config/LinuxServer/PalWorldSettings.ini", "[/Script/Pal.PalGameWorldSettings]\n"+
+		`OptionSettings=(Difficulty=None,ExpRate=1.000000,ServerName="Default Palworld Server",CrossplayPlatforms=(Steam,Xbox,PS5,Mac))`)
+	want := map[string]string{"Difficulty": "None", "ExpRate": "1.000000", "ServerName": "Default Palworld Server", "CrossplayPlatforms": "(Steam,Xbox,PS5,Mac)"}
+	if len(pal) != len(want) {
+		t.Fatalf("palworld: got %d settings: %+v", len(pal), pal)
+	}
+	for _, s := range pal {
+		if s.Section != "OptionSettings" || want[s.Key] != s.Value {
+			t.Errorf("palworld setting %+v", s)
+		}
+	}
+
+	// Minecraft's server.properties
+	mc := parseConfig("/data/server.properties", "#Minecraft server properties\nmax-players=20\nmotd=A Minecraft Server\nlevel-seed=\n")
+	if len(mc) != 3 || mc[0].Key != "max-players" || mc[0].Value != "20" || mc[2].Value != "" {
+		t.Errorf("properties: %+v", mc)
+	}
+
+	// INI sections and comments
+	ini := parseConfig("/server/x.ini", "; comment\n[ServerSettings]\nRCONPort = 27020\n[Other]\nKey=\"quoted\"\n")
+	if len(ini) != 2 || ini[0].Section != "ServerSettings" || ini[0].Value != "27020" || ini[1].Value != "quoted" {
+		t.Errorf("ini: %+v", ini)
+	}
+
+	// JSON, one level deep
+	js := parseConfig("/config/settings.json", `{"name":"x","limits":{"players":8},"tags":["a"]}`)
+	if len(js) != 3 || js[0].Key != "players" || js[0].Section != "limits" || js[0].Value != "8" {
+		t.Errorf("json: %+v", js)
+	}
+}
+
+func TestSuggestPattern(t *testing.T) {
+	for line, mustMatch := range map[string]string{
+		`[01:32:38 INFO]: Done (24.283s)! For help, type "help"`:                                      `[03:01:02 INFO]: Done (7.5s)! For help, type "help"`,
+		`[2026.10.25-03.10.36:455][  0]Server has completed startup and is now advertising for join.`: `[2026.10.26-11.00.00:001][ 12]Server has completed startup and is now advertising for join.`,
+		`2026-10-25T03:10:36Z Server started on port 7777`:                                            `2026-10-26T09:00:00Z Server started on port 8000`,
+	} {
+		p := suggestPattern(line)
+		if p == "" {
+			t.Errorf("no pattern for %q", line)
+			continue
+		}
+		re := regexp.MustCompile(p)
+		if !re.MatchString(line) || !re.MatchString(mustMatch) {
+			t.Errorf("pattern %q should match %q and %q", p, line, mustMatch)
+		}
+	}
+	if p := suggestPattern("[12:00:00] ok"); p != "" {
+		t.Errorf("too-short line gave pattern %q", p)
+	}
+}
+
+func TestAnalyzeLines(t *testing.T) {
+	r := &bootReport{}
+	analyzeLines(r, []logLine{
+		{At: 1, Source: "console", Text: "Starting server"},
+		{At: 2, Source: "console", Text: "Failed to load optional module"},
+		{At: 9, Source: "console", Text: "[09:00:01 INFO]: Done (8.1s)! For help, type \"help\""},
+		{At: 9, Source: "console", Text: "[09:00:01 INFO]: Thread RCON Listener started"},
+		// After the stop at 200s: the shutdown, as Minecraft's runner prints it
+		{At: 201, Source: "console", Text: "[06:01:39] [RCON Listener #1/INFO]: Thread RCON Client /0:0:0:0:0:0:0:1 started"},
+		{At: 202, Source: "console", Text: "2026-10-25T06:01:39.976Z\tINFO\tmc-server-runner\tDone"},
+	}, []logLine{{At: -1, Source: "/server/x.log", Text: "Listening on 0.0.0.0:7777"}}, 200)
+	if len(r.ErrorLines) != 1 {
+		t.Fatalf("errors %v", r.ErrorLines)
+	}
+	// The last ready line before the stop, not the shutdown's "Done"
+	if r.SuggestedExample != `[09:00:01 INFO]: Done (8.1s)! For help, type "help"` {
+		t.Errorf("example = %q", r.SuggestedExample)
+	}
+
+	// No console candidate: fall back to the first one in a log file
+	r = &bootReport{}
+	analyzeLines(r, []logLine{{At: 1, Source: "console", Text: "booting"}},
+		[]logLine{{At: -1, Source: "/server/a.log", Text: "Server has completed startup and is now advertising for join."},
+			{At: -1, Source: "/server/a.log", Text: "Server shutdown done"}}, 100)
+	if r.SuggestedExample != "Server has completed startup and is now advertising for join." {
+		t.Errorf("file fallback example = %q", r.SuggestedExample)
+	}
+}
+
+func TestConfigCandidates(t *testing.T) {
+	for rel, want := range map[string]bool{
+		"server.properties":                      true,
+		"Pal/Saved/Config/LinuxServer/x.ini":     true,
+		"ShooterGame/Saved/Logs/ShooterGame.log": true,
+		"steamapps/appmanifest_123.acf":          false,
+		"Engine/Config/BaseEngine.ini":           false,
+		"plugins/Geyser/config.yml":              false,
+		"world/level.dat":                        false,
+	} {
+		if got := isConfigCandidate(rel, 1000); got != want {
+			t.Errorf("isConfigCandidate(%q) = %v, want %v", rel, got, want)
+		}
+	}
+}