feat(editor): mode-driven shelf/column/spawn placement + cross-kind floor collision

Migrate the remaining floor-placed kinds onto the unified snapping/modifier
model and generalize floor collision so any solid floor kind blocks any other.

- shelf/column/spawn declare `snapProfile: 'item'` → contextual snapping chip,
  Shift=cycle, Ctrl=grid step during placement; their tools read the active
  mode (grid/lines/off) instead of legacy Shift/Alt bypass; spawn fresh
  placement now respects alignment ("lines") like its move.
- Resize/radial handles claim the handle-drag scope (new RESIZE_HANDLE_DRAG_LABEL)
  so the HUD shows no select-mode shortcuts mid-resize.
- Column move migrated to the generic MoveRegistryNodeTool (declare `movable`,
  drop the bespoke move-tool) — gains mode-driven snapping, alignment, R/T,
  slab lift, grid SFX, and the collision box for free. 2D move still routes
  through `floorplanMoveTarget`.
- Cross-kind floor collision: new declarative `FloorPlacedConfig.collides`
  (item/shelf/column opt in; spawn/MEP/stair stay off). `canPlaceOnFloor` now
  treats every colliding floor kind as an obstacle (was item-only), reading the
  declarative footprint; the generic move tool's red/green placement box gates
  on `collides`. Column footprint uses the visible `columnFootprintHalf` extent
  so the box/slab-lift/collision track the real (round/square) column size.

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

packages/core/src/registry/types.ts

@@ -1575,6 +1575,15 @@ export type FloorPlacedConfig = {
   footprint?: FloorPlacedFootprintResolver
   footprints?: FloorPlacedFootprintsResolver
   applies?: (node: AnyNode) => boolean
+  /**
+   * Opt this kind into floor-placement collision: its footprint blocks other
+   * placements (it's an obstacle in `canPlaceOnFloor`) AND its own
+   * placement/move refuses to overlap another colliding footprint (red ghost,
+   * Alt to force). Solid furniture-like kinds (item / shelf / column) set this;
+   * markers and port-mated kinds (spawn / MEP / stair) leave it off so they
+   * neither block nor get blocked. Default off.
+   */
+  collides?: boolean
 }
 
 /**