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/inspect.go

@@ -278,8 +278,8 @@ func parseProbe(f *imageFacts, out string) {
 }
 
 // suggestContainerUser works out whether the image only works as a specific user. Images either declare
-// it (USER) or are built around an account whose home folder nobody else may enter (ARK's gameserver,
-// uid 25000, with /home/gameserver at 700).
+// it (USER) or are built around an account whose home folder nobody else may enter (e.g. a home folder
+// at mode 700 owned by a uid other than 1000).
 func suggestContainerUser(f *imageFacts) {
 	if u := strings.TrimSpace(f.User); u != "" && u != "root" && u != "0" {
 		resolved := resolveUser(f, u)
@@ -364,7 +364,7 @@ func checkTemplate(game map[string]any, f *imageFacts) (problems, notes []string
 	}
 	if cmd, _ := game["defaultStartupCommand"].(string); cmd != "" {
 		for _, m := range assignedVars.FindAllStringSubmatch(cmd, -1) {
-			provided[m[1]] = true // set by the command itself, e.g. export ASA_START_PARAMS=...
+			provided[m[1]] = true // set by the command itself, e.g. export START_PARAMS=...
 		}
 		withDefault := map[string]bool{}
 		for _, m := range defaultedRef.FindAllStringSubmatch(cmd, -1) {
@@ -410,7 +410,7 @@ func containerPort(p string) string {
 	return p
 }
 
-// startupScriptPaths picks absolute paths out of a template's startup command (e.g. ARK's
+// startupScriptPaths picks absolute paths out of a template's startup command (e.g. an image's
 // /usr/bin/start_server) so the probe reads those scripts too.
 func startupScriptPaths(game map[string]any) []string {
 	cmd, _ := game["defaultStartupCommand"].(string)