fix: make inventory backpack visible by instancing in Game.tscn and fixing Tween API

- Add InventoryBackpack under HUD CanvasLayer (layer 5) in Game.tscn
- Add InventoryOverlay under InventoryOverlayLayer CanvasLayer (layer 10)
- Fix Tween.TRANS_SINE_IN -> .set_trans(TRANS_SINE).set_ease(EASE_IN) in
  InventoryBackpack.gd (Godot 4.6 split transition and easing APIs)

Game.tscn

@@ -10,6 +10,8 @@
 [ext_resource type="PackedScene" uid="uid://c0mp4a2u3jkd" path="res://portrait.tscn" id="7_fj12q"]
 [ext_resource type="Script" uid="uid://bsvab128vy1ip" path="res://OffsetCameraBasedOnMovement.gd" id="8_cvftx"]
 [ext_resource type="PackedScene" uid="uid://dyk4rcqsk3aed" path="res://scenes/kq4_003_fountain_pool/kq4_003_fountain_pool.tscn" id="8_yx171"]
+[ext_resource type="PackedScene" uid="uid://dxkyfas46q7ef" path="res://inventory/inventory_backpack/InventoryBackpack.tscn" id="9_backpack"]
+[ext_resource type="PackedScene" uid="uid://djoycn4xfa8p3" path="res://inventory/inventory_overlay/InventoryOverlay.tscn" id="a_overlay"]
 
 [sub_resource type="ShaderMaterial" id="ShaderMaterial_44mjr"]
 shader = ExtResource("2_jr51a")
@@ -183,3 +185,22 @@ label_settings = SubResource("LabelSettings_narrator")
 horizontal_alignment = 1
 vertical_alignment = 1
 autowrap_mode = 3
+
+[node name="HUD" type="CanvasLayer" parent="." unique_id=-294967295]
+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