feat(editor): node-declared per-context snapping + contextual HUD + painter scope

Generify the snapping/modifier HUD off the FSM scope and node declarations
instead of wall-creation-shaped, leaking pills.

- Per-context snapping (`snappingModeByContext`, persisted): wall / item /
  polygon mode-sets with exclusive modes (grid | lines | angles | off), each
  doing exactly what its chip says. Context is node-declared via the new
  `NodeDefinition.snapProfile` ('item' | 'structural'); the resolver maps
  (profile × action) → context with no per-kind switch.
- Scope-driven HUD: helper-manager reads the interaction scope; reshaping
  (endpoint/curve/boundary) and item move get their own chip, no select-hint
  leak. Rotate R/T rounds to 45°; Alt = force-place only (hidden for
  structural kinds); Shift = cycle everywhere.
- Slab/ceiling drafting: Shift=cycle, mode-aware grid/angle, Enter finishes
  (minDraftVertices); polygon boundary vertex/edge drag begins a reshaping
  scope. Fix grid/angle being ignored on boundary edit + slab creation:
  make resolveSurfacePlanPointSnap exclusive (alignment gated on magnetic) so
  grid/angles keep the snapped fallback instead of the raw cursor.
- Painter application scope: node-derived (single/object/matching/room) from
  the hovered node, cyclable via Shift, single-source HUD chip.
- Remove the redundant GridSnapControl from view-toggles (grid step lives in
  the contextual HUD now).

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

packages/nodes/src/ceiling/move-tool.tsx

@@ -16,6 +16,7 @@ import {
 import {
   CursorSphere,
   consumePlacementDragRelease,
+  isMagneticSnapActive,
   markToolCancelConsumed,
   triggerSFX,
   useAlignmentGuides,
@@ -37,7 +38,7 @@ import { BufferGeometry, DoubleSide, Path, Shape, ShapeGeometry, Vector3 } from
  * mesh's X/Z position on rebuild (`mesh.position.x = 0`,
  * `mesh.position.z = 0`) so the visual transitions smoothly.
  *
- * Snaps to the editor's configured grid step (Shift bypasses).
+ * Snaps to the editor's configured grid step.
  */
 function snap(value: number) {
   return snapScalar(value, useEditor.getState().gridSnapStep)
@@ -149,12 +150,10 @@ export const MoveCeilingTool: React.FC<{ node: CeilingNode }> = ({ node }) => {
 
     const onGridMove = (event: GridEvent) => {
       if (isFloorplanSourcedEvent(event)) return
-      const bypassSnap = event.nativeEvent?.shiftKey === true
-      const localX = bypassSnap ? event.localPosition[0] : snap(event.localPosition[0])
-      const localZ = bypassSnap ? event.localPosition[2] : snap(event.localPosition[2])
+      const localX = snap(event.localPosition[0])
+      const localZ = snap(event.localPosition[2])
 
       if (
-        !bypassSnap &&
         previousGridPosRef.current &&
         (localX !== previousGridPosRef.current[0] || localZ !== previousGridPosRef.current[1])
       ) {
@@ -170,8 +169,8 @@ export const MoveCeilingTool: React.FC<{ node: CeilingNode }> = ({ node }) => {
 
       // Figma-style alignment snap: align the ceiling's translated polygon
       // vertices to other objects' anchors; fold the snap into the delta and
-      // publish a guide. Alt bypasses alignment; Shift bypasses all snap.
-      const bypass = event.nativeEvent?.altKey === true || bypassSnap
+      // publish a guide. Alignment follows the global magnetic snap mode.
+      const bypass = !isMagneticSnapActive()
       if (!bypass && alignmentCandidates.length > 0) {
         const result = resolveAlignment({
           moving: polygonAnchors(ceilingId, translatePolygon(originalPolygon, deltaX, deltaZ)),