feat: Implement Phase 18 palette image icons and update asset card functionality

scripts/editors/stage/stage_chrome.gd

@@ -3,6 +3,14 @@ extends CanvasLayer
 ## Shared stage presentation shell. Domain decisions are reported to SandboxStage.
 
 const ASSET_CARD := preload("res://scripts/shared/ui/asset_card.gd")
+const PALETTE_ICON_TEXTURES: Dictionary = {
+	"ground": preload("res://resources/icons/ground.png"),
+	"ramp": preload("res://resources/icons/ramp.png"),
+	"step": preload("res://resources/icons/step.png"),
+	"prop": preload("res://resources/icons/prop.png"),
+	"stickman": preload("res://resources/icons/stickman.png"),
+	"area": preload("res://resources/icons/area.png"),
+}
 
 signal file_menu_requested(id: int)
 signal recent_menu_requested
@@ -496,8 +504,10 @@ func _build_palette(entries: Array[Dictionary]) -> void:
 	cards.size_flags_horizontal = Control.SIZE_EXPAND_FILL
 	scroll.add_child(cards)
 	for entry: Dictionary in entries:
-		var card: Variant = ASSET_CARD.new()
-		card.configure(entry, null, _stage_theme)
+		var card: AssetCard = ASSET_CARD.new() as AssetCard
+		var placement_id: String = String(entry.get("placement_id", ""))
+		var icon_texture: Texture2D = PALETTE_ICON_TEXTURES.get(placement_id) as Texture2D
+		card.configure(entry, icon_texture, _stage_theme)
 		card.toggle_mode = true
 		card.activated.connect(_on_palette_activated)
 		card.drag_started.connect(_on_palette_drag_started)