feat(builder): documented launch options only, and no game-specific code

Launch options must be documented. A draft passed an option its server
doesn't have; servers ignore unknown options, so it booted and passed every
boot test while its setting did nothing. build now reads the pages research
based the variant on, in full, and the drafter rejects any launch option in
the startup command that none of them, nor the image's own scripts, mention.
Shell tools' options (mkdir -p, [ -n ...]) are skipped; the check is off
without sources.

The builder is game-agnostic:
- AUTHORING.md (the model's rules), the research prompt and the schema
  describe the rules without naming a game.
- The draft prompt no longer includes real templates from the repo. Its
  format example is one invented server (no real command, options, ports or
  app id), checked by TestExampleTemplateFollowsTheRules.
- Comments, help texts, BUILDER.md and test fixtures use invented names and
  values.
- TestBuilderIsGameAgnostic reads every game's name and id from games/ and
  fails if any appears in the builder's code, tests, rules, schemas or docs.

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

cmd/gbrgames/agnostic_test.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// The builder must work the same for every game: no game's name, id or code in its source, its rules for
+// the model (AUTHORING.md), the schemas sent with every draft, or its docs. Games are read from games/,
+// so a newly merged template is covered as soon as it lands.
+func TestBuilderIsGameAgnostic(t *testing.T) {
+	root := filepath.Join("..", "..")
+	templates, _ := filepath.Glob(filepath.Join(root, "games", "*", "game.yaml"))
+	if len(templates) == 0 {
+		t.Fatal("no templates found to check against")
+	}
+	var names []string
+	for _, f := range templates {
+		g, err := loadMap(f)
+		if err != nil {
+			continue
+		}
+		for _, key := range []string{"id", "name"} {
+			if s, _ := g[key].(string); len(s) > 2 {
+				names = append(names, s)
+			}
+		}
+	}
+
+	files, _ := filepath.Glob("*.go")
+	files = append(files, filepath.Join(root, "AUTHORING.md"), filepath.Join(root, "BUILDER.md"))
+	schemas, _ := filepath.Glob(filepath.Join(root, "schema", "*.json"))
+	files = append(files, schemas...)
+	for _, f := range files {
+		raw, err := os.ReadFile(f)
+		if err != nil {
+			t.Fatal(err)
+		}
+		text := string(raw)
+		for _, n := range names {
+			re := regexp.MustCompile(`(?i)(^|[^A-Za-z0-9])` + regexp.QuoteMeta(n) + `($|[^A-Za-z0-9])`)
+			if loc := re.FindStringIndex(text); loc != nil {
+				line := strings.Count(text[:loc[0]], "\n") + 1
+				t.Errorf("%s:%d mentions %q: the builder must not name or copy any game", f, line, n)
+			}
+		}
+	}
+}