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>

tests/profiles/test_progress_updates.gd

@@ -83,8 +83,44 @@ func test_next_difficulty_for_unknown_skill_returns_current_difficulty() -> void
     assert_eq(ProgressUpdates.next_difficulty_for_skill(data, "inconnue", 2), 2)
 
 
-func test_add_stars_accumulates() -> void:
-    var data := _base_save()
-    data = ProgressUpdates.add_stars(data, 1)
-    data = ProgressUpdates.add_stars(data, 2)
+func test_first_mission_result_adds_its_stars_to_the_total() -> void:
+    var data := ProgressUpdates.record_mission_result(_base_save(), "mission_a", 2)
+    assert_eq(data["rewards"]["stars"], 2)
+    assert_eq(
+        data["mission_results"]["mission_a"], {"best_stars": 2, "last_stars": 2, "completions": 1}
+    )
+
+
+func test_replaying_a_mission_only_adds_the_improvement() -> void:
+    var data := ProgressUpdates.record_mission_result(_base_save(), "mission_a", 1)
+    data = ProgressUpdates.record_mission_result(data, "mission_a", 3)
+    assert_eq(data["rewards"]["stars"], 3, "1 puis 3 etoiles : 3 au total, pas 4")
+    assert_eq(data["mission_results"]["mission_a"]["best_stars"], 3)
+    assert_eq(data["mission_results"]["mission_a"]["completions"], 2)
+
+
+func test_a_worse_replay_never_lowers_the_best_score() -> void:
+    var data := ProgressUpdates.record_mission_result(_base_save(), "mission_a", 3)
+    data = ProgressUpdates.record_mission_result(data, "mission_a", 1)
     assert_eq(data["rewards"]["stars"], 3)
+    assert_eq(data["mission_results"]["mission_a"]["best_stars"], 3)
+    assert_eq(data["mission_results"]["mission_a"]["last_stars"], 1)
+
+
+func test_stars_of_different_missions_add_up() -> void:
+    var data := ProgressUpdates.record_mission_result(_base_save(), "mission_a", 2)
+    data = ProgressUpdates.record_mission_result(data, "mission_b", 3)
+    assert_eq(data["rewards"]["stars"], 5)
+
+
+func test_grant_items_never_duplicates() -> void:
+    var ids: Array[String] = ["item_a", "item_b"]
+    var data := ProgressUpdates.grant_items(_base_save(), ids)
+    data = ProgressUpdates.grant_items(data, ids)
+    assert_eq(data["rewards"]["items"], ["item_a", "item_b"])
+
+
+func test_record_mission_result_validates_against_the_save_schema() -> void:
+    var data := ProgressUpdates.record_mission_result(_base_save(), "mission_a", 2)
+    var errors := SchemaValidator.validate(data, DataLoader.load_schema("save"))
+    assert_eq(errors, [])

tests/profiles/test_save_migration.gd

@@ -3,12 +3,26 @@ extends GutTest
 
 
 func test_current_version_is_returned_unchanged() -> void:
-    var data := {"schema_version": 1, "profile_id": "profile_test"}
+    var data := {"schema_version": 2, "profile_id": "profile_test", "mission_results": {}}
     var migrated := SaveMigration.migrate(data)
-    assert_eq(migrated["schema_version"], 1)
+    assert_eq(migrated["schema_version"], 2)
     assert_eq(migrated["profile_id"], "profile_test")
 
 
+func test_version_1_save_gains_empty_mission_results_and_keeps_its_stars() -> void:
+    var data := SaveFactory.new_save("profile_test", "Explorateur", "CE1")
+    data["schema_version"] = 1
+    data.erase("mission_results")
+    data["rewards"] = {"stars": 4, "items": ["item_a"]}
+
+    var migrated := SaveMigration.migrate(data)
+
+    assert_eq(migrated["schema_version"], 2)
+    assert_eq(migrated["mission_results"], {})
+    assert_eq(migrated["rewards"], {"stars": 4, "items": ["item_a"]})
+    assert_eq(SchemaValidator.validate(migrated, DataLoader.load_schema("save")), [])
+
+
 func test_missing_version_is_rejected() -> void:
     var data := {"profile_id": "profile_test"}
     assert_eq(SaveMigration.migrate(data), {})