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/world/world_map.gd

@@ -7,19 +7,23 @@ extends Control
 ## peut basculer sur la carte CE1 pour revoir les notions precedentes.
 
 const MARKER_HALF_WIDTH := 80.0
-const MARKER_HALF_HEIGHT := 36.0
+const MARKER_HALF_HEIGHT := 48.0
 
 var _viewed_level := "CE1"
 
 @onready var _title_label: Label = %TitleLabel
 @onready var _map_area: Control = %MapArea
 @onready var _level_toggle_button: Button = %LevelToggleButton
+@onready var _total_stars_label: Label = %TotalStarsLabel
+@onready var _collection_button: Button = %CollectionButton
 
 
 func _ready() -> void:
     _viewed_level = ProgressManager.school_level()
     _level_toggle_button.visible = _viewed_level == "CE2"
     _level_toggle_button.pressed.connect(_on_level_toggle_pressed)
+    _collection_button.text = UIText.get_text("world_map.collection_button")
+    _collection_button.pressed.connect(_on_collection_pressed)
     _refresh()
 
 
@@ -30,6 +34,9 @@ func _refresh() -> void:
         "world_map.review_ce1_button" if _viewed_level == "CE2" else "world_map.back_to_ce2_button"
     )
     _level_toggle_button.text = UIText.get_text(toggle_key)
+    _total_stars_label.text = (
+        "%s %d" % [UIText.get_text("world_map.total_stars_label"), ProgressManager.stars()]
+    )
     _populate_missions()
 
 
@@ -42,6 +49,10 @@ func _populate_missions() -> void:
         _map_area.add_child(_build_marker(mission))
 
 
+func _on_collection_pressed() -> void:
+    GameManager.goto(GameManager.SCENE_COLLECTION)
+
+
 func _on_level_toggle_pressed() -> void:
     _viewed_level = "CE1" if _viewed_level == "CE2" else "CE2"
     _refresh()
@@ -49,7 +60,17 @@ func _on_level_toggle_pressed() -> void:
 
 func _build_marker(mission: Dictionary) -> Control:
     var button := Button.new()
-    button.text = "%s\n%s" % [mission["title"], _status_label_for(mission)]
+    button.autowrap_mode = TextServer.AUTOWRAP_WORD_SMART
+    button.text = (
+        "%s\n%s\n%s %d/%d"
+        % [
+            mission["title"],
+            _status_label_for(mission),
+            UIText.get_text("world_map.mission_stars_label"),
+            ProgressManager.mission_best_stars(mission["mission_id"]),
+            MissionScoring.MAX_STARS,
+        ]
+    )
 
     var map_position: Dictionary = mission["map_position"]
     var x: float = map_position["x"]