The viewer threads the model's doc through normalizeModel into both
composite view states — appended to INFO.B (collapsed box) and INFO.C
(expanded cluster frame) — and shows the root composite's doc as a muted
header line (#rootdoc span in GRAPH_HEAD, empty when absent; the DOM
population sits in the browser-only block, the same boundary as the
breadcrumb). viewer_tooltip.mjs pins the doc'd cases beside the
byte-exact un-doc'd pins; sample-model.json gains the additive doc key;
e2e drives aura graph over a nested-doc blueprint into the emitted page.
closes#125
