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>
