Editor: interactive composition wireframe — drag to reorder and restructure

Drag a view's box (or Alt+up/down) to reorder it within its container; drag onto another view's edge to pair the two in a new row/column, move across containers, or insert. Each leaf shows a glyph of its mark type.

Core: spec-restructure.wrapViews (wrap, with flatten-to-insert, collapse, and data-pin invariants) and spec-insert.moveViewTo; the editor applies every drag as one undoable edit via AppStore.composeRequest, keeping the editor the single text source.

docs/architecture/09-visual-design.md

@@ -371,6 +371,14 @@ notifications/validation as they arrive):
 | Success | `CheckmarkFilled`    | `--support-success`     | `Toaster` (success)                         |
 | Info    | `InformationFilled`  | `--support-info`        | `Toaster` (info)                            |
 
+**Mark set** — a custom `mark-*` sub-family, one simplified glyph per Vega-Lite mark
+(bar, line, area, point, arc, rect, tick, rule, text, plus a `mark-generic` fallback),
+drawn on the same 32-grid (stroked where a line reads truer than a fill). It labels the
+leaves of the composition wireframe so views read apart at a glance; mark synonyms
+(circle/square → point, trail → line, image → rect) collapse onto it via `markIconName`
+(`mark-icon.ts`), and an unknown or absent mark falls to `mark-generic`. Decorative there
+(the box's `aria-label` names the view), so these are not in the ⭐ icon-only set.
+
 **Scoped set** — single-surface, glyph **reserved** in the ledger but **not yet in
 the `Icon` registry**: