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>

tools/screenshot.gd

@@ -0,0 +1,72 @@
+extends SceneTree
+## Outil de developpement : charge une scene, attend quelques images puis
+## enregistre le rendu en PNG. Usage (fenetre reelle, pas --headless) :
+##   godot --path . --resolution 1152x648 -s res://tools/screenshot.gd -- \
+##       res://scenes/world/world_map.tscn out.png [CE1|CE2] [mission_id]
+## Cree un profil temporaire pour que les scenes qui lisent la progression
+## fonctionnent, puis le supprime.
+
+
+func _initialize() -> void:
+    var args := OS.get_cmdline_user_args()
+    var scene_path: String = args[0]
+    var out_path: String = args[1]
+    var level: String = args[2] if args.size() > 2 else "CE1"
+
+    var profiles: Node = root.get_node("ProfileManager")
+    var game: Node = root.get_node("GameManager")
+    var profile_id: String = profiles.call("create_profile", "Capture", level)
+    profiles.call("select_profile", profile_id)
+    if args.size() > 3:
+        game.set("pending_mission_id", args[3])
+
+    for arg in args:
+        if arg.begins_with("outcomes:"):
+            var typed: Array[String] = []
+            for part in arg.trim_prefix("outcomes:").split(","):
+                typed.append(part)
+            game.set("last_outcomes", typed)
+
+    var scene: Node = load(scene_path).instantiate()
+    root.add_child(scene)
+    for i in 5:
+        await process_frame
+    # Actions optionnelles sur exercise_host, a partir du 5e argument :
+    #   continue_rule | answer:<index> | toggle:<index> | type:<texte> | validate
+    #   | continue_feedback
+    for action in args.slice(4):
+        if action.begins_with("outcomes:"):
+            continue
+        await _run_action(scene, action)
+        for i in 5:
+            await process_frame
+    for i in 90:
+        await process_frame
+    var image := root.get_texture().get_image()
+    image.save_png(out_path)
+    profiles.call("delete_profile", profile_id)
+    quit(0)
+
+
+func _run_action(scene: Node, action: String) -> void:
+    var overlay: Node = scene.get_node("%OverlayContainer")
+    var exercise: Node = scene.get_node("%ExerciseContainer").get_child(0) if scene.get_node("%ExerciseContainer").get_child_count() > 0 else null
+    var parts := action.split(":", true, 1)
+    match parts[0]:
+        "continue_rule":
+            overlay.get_child(0).emit_signal("continued")
+        "answer":
+            exercise.emit_signal("answer_submitted", int(parts[1]))
+        "toggle":
+            exercise.get_node("%TokensBox").get_child(int(parts[1])).emit_signal("toggled", true)
+        "type":
+            var field: LineEdit = (
+                exercise.get_node("%TextEdit")
+                if exercise.has_node("%TextEdit")
+                else exercise.get_node("%CorrectionsBox").get_child(0)
+            )
+            field.text = parts[1]
+        "validate":
+            exercise.get_node("%ValidateButton").emit_signal("pressed")
+        "continue_feedback":
+            overlay.get_child(overlay.get_child_count() - 1).get_node("%ContinueButton").emit_signal("pressed")