Add mission scoring, rewards collection and save schema v2

Phase "score et récompenses" of the post-0.1.0 plan (user feedback:
wants a more game-like experience with scoring and rewards).

- MissionScoring: 1-3 stars from how each exercise was solved (never
  speed; a finished mission always gives at least one star).
- Save schema v2: mission_results (best/last stars, completions) with a
  v1->v2 migration that keeps existing stars and items.
- Total only grows by the improvement over a mission's best score.
- Data-driven collection (data/rewards, reward_item schema, validated
  incl. mission cross-check) unlocked by RewardRules.
- Reward screen, collection screen, stars on the world map.
- Version 0.2.0.

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

scenes/ui/reward_screen.gd

@@ -1,28 +1,60 @@
 extends Control
-## Ecran de recompense : une mission terminee rapporte toujours la meme
-## recompense, que l'enfant ait eu besoin d'aide ou non (cahier des charges
-## §2, principe 6 : pas de recompense liee a la vitesse ou a la performance).
-## Sauvegarde groupee ici, en fin de mission (docs/specs/decisions.md point 7).
-
-const STARS_PER_MISSION := 1
+## Ecran de fin de mission : etoiles gagnees (1 a 3, selon la reussite et
+## l'aide utilisee, jamais selon la vitesse : cahier des charges §2), total,
+## nouveaux objets de la collection. Une mission terminee rapporte toujours
+## au moins une etoile. Sauvegarde groupee ici, en fin de mission
+## (docs/specs/decisions.md point 7).
 
 @onready var _title_label: Label = %TitleLabel
 @onready var _stars_label: Label = %StarsLabel
+@onready var _message_label: Label = %MessageLabel
+@onready var _record_label: Label = %RecordLabel
+@onready var _total_label: Label = %TotalLabel
+@onready var _new_items_label: Label = %NewItemsLabel
+@onready var _collection_button: Button = %CollectionButton
 @onready var _continue_button: Button = %ContinueButton
 
 
 func _ready() -> void:
-    ProgressManager.add_stars(STARS_PER_MISSION)
+    var summary := ProgressManager.complete_mission(
+        GameManager.pending_mission_id, GameManager.last_outcomes
+    )
     ProgressManager.save_now()
 
     _title_label.text = UIText.get_text("reward_screen.title")
-    _stars_label.text = "%s %d" % [
-        UIText.get_text("reward_screen.stars_label"), ProgressManager.stars()
-    ]
+    _stars_label.text = (
+        "%s %d/%d"
+        % [UIText.get_text("reward_screen.stars_label"), summary["stars"], MissionScoring.MAX_STARS]
+    )
+    _message_label.text = UIText.get_text("reward_screen.message_%d" % summary["stars"])
+    _record_label.text = UIText.get_text("reward_screen.record_label")
+    _record_label.visible = summary["is_record"]
+    _total_label.text = (
+        "%s %d" % [UIText.get_text("reward_screen.total_label"), summary["total_stars"]]
+    )
+
+    var new_items: Array = summary["new_items"]
+    _new_items_label.visible = not new_items.is_empty()
+    if not new_items.is_empty():
+        var titles: Array[String] = []
+        for item in ExerciseEngine.get_reward_items():
+            if new_items.has(item["item_id"]):
+                titles.append(item["title"])
+        _new_items_label.text = (
+            "%s\n%s" % [UIText.get_text("reward_screen.new_items_label"), "\n".join(titles)]
+        )
+
+    _collection_button.text = UIText.get_text("reward_screen.collection_button")
+    _collection_button.pressed.connect(_on_collection_pressed)
     _continue_button.text = UIText.get_text("reward_screen.continue_button")
     _continue_button.pressed.connect(_on_continue_pressed)
 
 
+func _on_collection_pressed() -> void:
+    GameManager.pending_mission_id = ""
+    GameManager.goto(GameManager.SCENE_COLLECTION)
+
+
 func _on_continue_pressed() -> void:
     GameManager.pending_mission_id = ""
     GameManager.goto(GameManager.SCENE_WORLD_MAP)