fix: wire backpack signals and simplify positioning

- Connect overlay_show_requested/overlay_hide_requested signals in Game.tscn
  to new handlers in MainGame.gd that call show_overlay()/hide_overlay()
- Simplify backpack to fixed 70x70 position at top-left (layout_mode=0)
- Remove broken anchor overrides from Game.tscn that were anchoring to bottom

Game.tscn

@@ -190,17 +190,11 @@ autowrap_mode = 3
 layer = 5
 
 [node name="InventoryBackpack" parent="HUD" unique_id=-294967294 instance=ExtResource("9_backpack")]
-anchors_preset = 12
-anchor_top = 1.0
-anchor_bottom = 1.0
-offset_top = -64.65503
-offset_bottom = -4.654907
-grow_vertical = 0
 
 [node name="InventoryOverlayLayer" type="CanvasLayer" parent="." unique_id=-294967293]
 layer = 10
-visible = false
 
 [node name="InventoryOverlay" parent="InventoryOverlayLayer" unique_id=-294967292 instance=ExtResource("a_overlay")]
-grow_horizontal = 2
-grow_vertical = 2
+
+[connection signal="overlay_show_requested" from="HUD/InventoryBackpack" to="HUD/InventoryBackpack/.." method="_on_backpack_show_overlay"]
+[connection signal="overlay_hide_requested" from="HUD/InventoryBackpack" to="HUD/InventoryBackpack/.." method="_on_backpack_hide_overlay"]

MainGame.gd

@@ -74,6 +74,12 @@ func restore_cursor() -> void:
 func _unhandled_input(event: InputEvent) -> void:
 	$SceneViewport.push_input(event)
 	
+func _on_backpack_show_overlay() -> void:
+	$HUD/InventoryOverlay.show_overlay()
+
+func _on_backpack_hide_overlay() -> void:
+	$HUD/InventoryOverlay.hide_overlay()
+
 func _input(event):
 	if event.is_action_released("quit"):
 		get_tree().quit()

inventory/inventory_backpack/InventoryBackpack.tscn

@@ -3,11 +3,8 @@
 [ext_resource type="Script" uid="uid://2x3g0ethsdcgo" path="res://inventory/inventory_backpack/InventoryBackpack.gd" id="1"]
 
 [node name="InventoryBackpack" type="Control" unique_id=1000000001]
-layout_mode = 3
-anchors_preset = 2
-anchor_right = 1.0
-offset_top = 10.0
-offset_right = -70.0
+layout_mode = 0
+offset_right = 70.0
 offset_bottom = 70.0
 script = ExtResource("1")