fix(atlas): UX polish — stage-06 plain nodes + shorter arrow labels (#7)

Stage 06 no longer renders bare in Plain: Build is now tolerant of a jobless/
absent workflow (keeps an authored plain placeholder instead of erroring), and
generated CI job nodes carry a plain hint. Shortened the two overlong transition
labels ("Order written, sealed, agent-ready" → "Sealed & agent-ready",
"Agents produced a change" → "Change proposed") so they stop clipping.

Build tolerance test-first. build/vet/lint(0)/test green; screenshot-verified.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/atlas/model.go

@@ -64,12 +64,12 @@ func Build(atlasJSON, workflow []byte) (Atlas, error) {
 			continue
 		}
 		jobs, err := JobsFromWorkflow(workflow)
-		if err != nil {
-			return Atlas{}, fmt.Errorf("stage %s: %w", a.Stages[i].No, err)
+		if err != nil || len(jobs) == 0 {
+			continue // no CI job list available — keep the authored plain placeholder
 		}
 		nodes := make([]Node, 0, len(jobs))
 		for _, j := range jobs {
-			nodes = append(nodes, Node{Title: j})
+			nodes = append(nodes, Node{Title: j, Plain: "An automated check that must pass."})
 		}
 		a.Stages[i].Nodes = nodes
 	}