fix(ui): restore STANCE_ICONS constant removed during refactor

Startup crash — preload loop referenced STANCE_ICONS but the constant
was accidentally dropped when rewriting the icon cache logic.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/ui/stance_indicator.gd

@@ -10,6 +10,13 @@ const STANCE_COLORS := {
 	"Crouch": Color("#e8c547"),  # Amber — very quiet, slow
 }
 
+const STANCE_ICONS := {
+	"Sprint": "res://assets/icons/icon_stance_sprint.svg",
+	"Walk": "res://assets/icons/icon_stance_walk.svg",
+	"Careful": "res://assets/icons/icon_stance_careful.svg",
+	"Crouch": "res://assets/icons/icon_stance_crouch.svg",
+}
+
 var _current_stance: String = "Walk"
 var _panel: ImplantPanel
 var _icon: TextureRect