feat(editor): door/window placement-feel polish + placement-state refactor (#411)

Round 8 of the opening-placement UX work. Make door/window placement feel
physical and predictable, and unify the validity/placement logic behind one
shared decision.

UX:
- Window default sill 0.5 m (DEFAULT_WINDOW_SILL_M) so fresh windows float
  slightly above the floor; existing windows keep their own sill.
- Dev-only floor "shadow" projection for windows during placement/move
  (footprint + dashed drop-line) so an elevated window's plan spot is legible.
- Move SFX: one soft grid-snap click per grid step — identical free-following
  over floor or sliding on a wall (keyed on the raw cursor; per-frame + step
  dedup), no separate snap cue (that was a "double"). Mirrored into the 2D
  floorplan-move so 2D and 3D match.
- Shift = force-place over a collision (commit allowed; ghost stays a red
  warning) + free-place (lands at the raw cursor but keeps the alignment guides
  visible). Tint flips green/red live when Shift is pressed/released stationary.
- On-wall preview is now the tinted ghost (green placeable / red colliding),
  matching the free-follow ghost, instead of a pale solid mesh + thin wireframe.
- R-flip fixes: always toggles (no initial no-op needing a second press),
  e.repeat filtered, ghost rebuilds with the live `side`, and the ghost's
  on-wall world yaw uses `itemRotation - wallAngle` so it faces exactly what
  commit places (cursorRotation was π off for the asymmetric ghost). R ownership
  follows the current pointer pane (capture-phase + stopImmediatePropagation in
  the 2D overlay) so 3D and 2D never double-flip or go dead.

Refactor / quality:
- New `resolveOpeningPlacement({collides,forcePlace}) -> {placeable,tint}` in
  shared/wall-attach-target.ts — the single source of truth the ghost tint AND
  the commit gates both consume, so they can't disagree under Shift.
- Consolidated the byte-identical `hasWallChildOverlap` into one shared impl
  (door-math/window-math re-export it).
- applyGhost gained a green "valid" tint.
- Removed dead `cursorRotation` from the move-tool targets after the yaw fix.

Docs: "2D <-> 3D behavioral parity" principle in wiki/architecture/tools.md
(+ README + AGENTS.md) — applicable behaviors must exist in both views.

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

packages/nodes/src/shared/ghost-materials.ts

@@ -3,6 +3,7 @@
 import type { Material, Mesh, Object3D, Raycaster } from 'three'
 
 export const INVALID_GHOST_COLOR = 0xef_44_44
+export const VALID_GHOST_COLOR = 0x22_c5_5e
 
 const NO_RAYCAST = (_raycaster: Raycaster, _intersects: unknown[]) => {}
 
@@ -12,8 +13,11 @@ const NO_RAYCAST = (_raycaster: Raycaster, _intersects: unknown[]) => {}
  * Traverses the object tree, disables raycasting on all descendants (prevents
  * cursor-ray starvation), and clones visible mesh materials to set translucency.
  *
- * When `invalid` is true, sets color/emissive to INVALID_GHOST_COLOR and opacity ~0.4.
- * Otherwise sets opacity ~0.5 while preserving the original color.
+ * Tint by state:
+ *   - `invalid` (red, opacity ~0.4): off-host or colliding — can't place here.
+ *   - `valid` (green, opacity ~0.45): on a host and placeable — the "go" cue.
+ *   - neither (opacity ~0.5, original color): a plain translucent preview.
+ * `invalid` wins if both are passed.
  *
  * Skips: meshes whose material.visible === false (door/window root hitbox) and
  * children named 'cutout'.
@@ -21,11 +25,15 @@ const NO_RAYCAST = (_raycaster: Raycaster, _intersects: unknown[]) => {}
  * Returns cleanup that disposes only the cloned materials (never originals or geometry).
  *
  * @param root - The preview mesh tree (typically from buildDoorPreviewMesh / buildWindowPreviewMesh)
- * @param opts - { invalid?: boolean } whether to tint red for invalid placement
+ * @param opts - { invalid?, valid? } placement-state tint
  * @returns Cleanup function that disposes the cloned materials
  */
-export function applyGhost(root: Object3D, opts?: { invalid?: boolean }): () => void {
+export function applyGhost(
+  root: Object3D,
+  opts?: { invalid?: boolean; valid?: boolean },
+): () => void {
   const invalid = opts?.invalid ?? false
+  const valid = !invalid && (opts?.valid ?? false)
   const cloned: Material[] = []
 
   root.traverse((obj) => {
@@ -51,6 +59,12 @@ export function applyGhost(root: Object3D, opts?: { invalid?: boolean }): () =>
           INVALID_GHOST_COLOR,
         )
         clone.opacity = 0.4
+      } else if (valid) {
+        ;(clone as { color?: { setHex: (c: number) => void } }).color?.setHex(VALID_GHOST_COLOR)
+        ;(clone as { emissive?: { setHex: (c: number) => void } }).emissive?.setHex(
+          VALID_GHOST_COLOR,
+        )
+        clone.opacity = 0.45
       } else {
         clone.opacity = 0.5
       }