Bug-triage patch — fix torch builds, idle-pawn traps, floor render order

Three playtest-reported bugs fixed out-of-phase before Phase 18:

* Furniture build-queue gap: Torch / Bed / Crate / Workbench / CremationPyre
  were missing World.register_build_site(self) in _ready, so newly-painted
  designations never entered ConstructionProvider's iteration. The seeded
  cabin pre-built everything via _spawn_complete_* helpers, masking the gap
  until a player painted a fresh furniture designation.

* Wall-trap regression for bystanders + walk-through pawns: Wall._complete
  now dislodges any pawn on the tile via new Pathfinder.find_nearest_walkable
  BFS helper; Pawn._advance_walk re-checks next tile walkability before
  stepping, aborts walk + cancels job + lets Decision reroute. Phase 6's
  adjacent-stand fix only protected the BUILDING pawn.

* Floor / Pawn Y-sort ambiguity: Floor was anchored at tile-center
  (same Y as Pawn), so Y-sort tiebreak fell to scene-tree order and
  Floor (spawned later) drew over Pawn. Moved Floor origin to top-of-tile
  so Floor.y < Pawn.y under Y-sort; _draw rect offsets compensate.

All three verified via MCP runtime: torch built end-to-end, all 3 pawns
working on different jobs with no idle traps, pawn renders over floor.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scenes/world/crate.gd

@@ -77,11 +77,13 @@ func _ready() -> void:
 	accepted_types = []
 	# Register with the World stockpile pool so HaulingProvider sees us.
 	World.register_stockpile(self)
+	World.register_build_site(self)
 	queue_redraw()
 
 
 func _exit_tree() -> void:
 	World.unregister_stockpile(self)
+	World.unregister_build_site(self)
 
 
 ## One-shot initialiser called by the spawning / placement code.

scenes/world/pathfinder.gd

@@ -51,6 +51,33 @@ func is_walkable(cell: Vector2i) -> bool:
 	return _astar.is_in_boundsv(cell) and not _astar.is_point_solid(cell)
 
 
+## BFS outward from `cell` for the nearest walkable tile. Used to dislodge a
+## pawn trapped on a tile that just became impassable (e.g. another pawn built
+## a wall on top of them). Returns `cell` itself if no walkable tile is found
+## within `max_radius` (BFS-ring distance).
+func find_nearest_walkable(cell: Vector2i, max_radius: int = 8) -> Vector2i:
+	if is_walkable(cell):
+		return cell
+	var visited := {cell: true}
+	var frontier: Array[Vector2i] = [cell]
+	var offsets: Array[Vector2i] = [
+		Vector2i(0, -1), Vector2i(1, 0), Vector2i(0, 1), Vector2i(-1, 0),
+	]
+	for _ring in max_radius:
+		var next: Array[Vector2i] = []
+		for c in frontier:
+			for off in offsets:
+				var n: Vector2i = c + off
+				if visited.has(n):
+					continue
+				visited[n] = true
+				if is_walkable(n):
+					return n
+				next.append(n)
+		frontier = next
+	return cell
+
+
 ## Returns the path from `from` to `to` as tile-coordinate steps.
 ## The returned array EXCLUDES `from` and INCLUDES `to`.
 ## Returns an empty Array[Vector2i] when: