Visual overhaul: theme, illustrations, redesigned screens (0.3.0)

Phase "habillage" of the post-0.1.0 plan. Rendering was reviewed on real
screenshots (new tools/screenshot.gd, `make screenshot`), which also
caught and fixed map markers overlapping and truncated titles.

- Global Godot theme (Atkinson Hyperlegible font, cream/green/gold
  palette, raised buttons, rounded cards, thick keyboard focus).
- Original vector art: forest/marsh backdrops, Plume the owl, stars,
  exercise-type icons, correct/try-again icons, 10 collection items.
- Redesigned world map (markers as cards with icon, title and stars,
  responsive layout), profile screens, mission intro, exercise host,
  rule/feedback panels, reward screen and collection grid.
- Motion helper (pop-in, fade) honouring an animations setting.
- Settings: animations flag; base window 1152x648 with canvas_items.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scenes/ui/reward_screen.tscn

@@ -1,6 +1,8 @@
-[gd_scene load_steps=2 format=3]
+[gd_scene load_steps=4 format=3]
 
 [ext_resource type="Script" path="res://scenes/ui/reward_screen.gd" id="1"]
+[ext_resource type="PackedScene" path="res://scenes/ui/backdrop.tscn" id="backdrop"]
+[ext_resource type="Texture2D" path="res://assets/characters/owl_plume.svg" id="3"]
 
 [node name="RewardScreen" type="Control"]
 layout_mode = 3
@@ -11,59 +13,104 @@ grow_horizontal = 2
 grow_vertical = 2
 script = ExtResource("1")
 
-[node name="CenterContainer" type="CenterContainer" parent="."]
+[node name="Backdrop" parent="." instance=ExtResource("backdrop")]
 layout_mode = 1
 anchors_preset = 15
 anchor_right = 1.0
 anchor_bottom = 1.0
 grow_horizontal = 2
 grow_vertical = 2
-
-[node name="VBox" type="VBoxContainer" parent="CenterContainer"]
-layout_mode = 2
-theme_override_constants/separation = 20
-
-[node name="TitleLabel" type="Label" parent="CenterContainer/VBox"]
 unique_name_in_owner = true
-layout_mode = 2
-theme_override_font_sizes/font_size = 36
-horizontal_alignment = 1
 
-[node name="StarsLabel" type="Label" parent="CenterContainer/VBox"]
+[node name="Margin" type="MarginContainer" parent="."]
+layout_mode = 1
+anchors_preset = 15
+anchor_right = 1.0
+anchor_bottom = 1.0
+grow_horizontal = 2
+grow_vertical = 2
+theme_override_constants/margin_left = 32
+theme_override_constants/margin_top = 24
+theme_override_constants/margin_right = 32
+theme_override_constants/margin_bottom = 24
+
+[node name="Center" type="CenterContainer" parent="Margin"]
+layout_mode = 2
+
+[node name="Card" type="PanelContainer" parent="Margin/Center"]
+layout_mode = 2
+custom_minimum_size = Vector2(720, 0)
+
+[node name="VBox" type="VBoxContainer" parent="Margin/Center/Card"]
+layout_mode = 2
+theme_override_constants/separation = 12
+
+[node name="TitleLabel" type="Label" parent="Margin/Center/Card/VBox"]
 unique_name_in_owner = true
+theme_type_variation = &"CardTitle"
 layout_mode = 2
 horizontal_alignment = 1
 
-[node name="MessageLabel" type="Label" parent="CenterContainer/VBox"]
+[node name="StarsRow" type="HBoxContainer" parent="Margin/Center/Card/VBox"]
+unique_name_in_owner = true
+layout_mode = 2
+alignment = 1
+theme_override_constants/separation = 10
+
+[node name="StarsLabel" type="Label" parent="Margin/Center/Card/VBox"]
+unique_name_in_owner = true
+theme_type_variation = &"Emphasis"
+layout_mode = 2
+horizontal_alignment = 1
+
+[node name="MessageLabel" type="Label" parent="Margin/Center/Card/VBox"]
 unique_name_in_owner = true
 layout_mode = 2
 horizontal_alignment = 1
 autowrap_mode = 2
-custom_minimum_size = Vector2(480, 0)
 
-[node name="RecordLabel" type="Label" parent="CenterContainer/VBox"]
+[node name="RecordLabel" type="Label" parent="Margin/Center/Card/VBox"]
+unique_name_in_owner = true
+theme_type_variation = &"Emphasis"
+layout_mode = 2
+horizontal_alignment = 1
+
+[node name="TotalLabel" type="Label" parent="Margin/Center/Card/VBox"]
 unique_name_in_owner = true
 layout_mode = 2
 horizontal_alignment = 1
 
-[node name="TotalLabel" type="Label" parent="CenterContainer/VBox"]
+[node name="NewItemsBox" type="VBoxContainer" parent="Margin/Center/Card/VBox"]
 unique_name_in_owner = true
 layout_mode = 2
-horizontal_alignment = 1
+theme_override_constants/separation = 6
 
-[node name="NewItemsLabel" type="Label" parent="CenterContainer/VBox"]
+[node name="NewItemsLabel" type="Label" parent="Margin/Center/Card/VBox/NewItemsBox"]
 unique_name_in_owner = true
+theme_type_variation = &"Emphasis"
 layout_mode = 2
 horizontal_alignment = 1
 autowrap_mode = 2
-custom_minimum_size = Vector2(480, 0)
 
-[node name="CollectionButton" type="Button" parent="CenterContainer/VBox"]
+[node name="NewItemsRow" type="HBoxContainer" parent="Margin/Center/Card/VBox/NewItemsBox"]
 unique_name_in_owner = true
 layout_mode = 2
-custom_minimum_size = Vector2(200, 56)
+alignment = 1
+theme_override_constants/separation = 16
 
-[node name="ContinueButton" type="Button" parent="CenterContainer/VBox"]
+[node name="Buttons" type="HBoxContainer" parent="Margin/Center/Card/VBox"]
+layout_mode = 2
+theme_override_constants/separation = 16
+
+[node name="CollectionButton" type="Button" parent="Margin/Center/Card/VBox/Buttons"]
+unique_name_in_owner = true
+theme_type_variation = &"SecondaryButton"
+layout_mode = 2
+size_flags_horizontal = 3
+custom_minimum_size = Vector2(0, 56)
+
+[node name="ContinueButton" type="Button" parent="Margin/Center/Card/VBox/Buttons"]
 unique_name_in_owner = true
 layout_mode = 2
-custom_minimum_size = Vector2(200, 56)
+size_flags_horizontal = 3
+custom_minimum_size = Vector2(0, 56)