feat(builder): launch options must appear in the research sources

The Valheim draft in #13 passed -maxplayers, an option Valheim doesn't have.
The server ignores unknown options, so the draft booted and passed every
boot test while its MaxPlayers 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. The model gets it back to remove or
spell correctly. Options of shell tools (mkdir -p, [ -n ...]) are skipped.
The check is off when there are no sources (draft run by hand, no reader).

Against #13's 11 real sources it flags -maxplayers and nothing else.

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

cmd/gbrgames/draft.go

@@ -82,6 +82,9 @@ type draftJob struct {
 	Report              *bootReport
 	Provider, Model     string
 	NoPull              bool
+	// Text of the pages research based the variant on; when set, every launch option in the startup
+	// command must appear in it (or in the image's scripts)
+	Docs string
 }
 
 // drafter holds one conversation with the model about one game, so later problems (a failed boot) can
@@ -200,6 +203,7 @@ func (d *drafter) check(answer string) []string {
 			problems = append(problems, savesOutsideVolumes(g, d.job.Report)...)
 			problems = append(problems, splitSettings(g)...)
 			problems = append(problems, portSettings(g)...)
+			problems = append(problems, undocumentedOptions(g, d.job.Docs, d.facts)...)
 		}
 	}
 	return problems