Add the playable scene loop: boot through mission to reward

Wires every autoload up to a real UI: boot -> profile select/create
-> world map (three mission markers, positioned from data, not
hardcoded pixels) -> mission intro (narrative from data/missions/,
a new data type with its own schema) -> rule panel -> exercise host
-> one of the three exercise type scenes -> feedback panel -> reward
screen -> back to the map.

exercise_host is the only piece with real orchestration logic: picks
exercises via ExerciseEngine (now fully implemented, validating at
load like make validate-data does), validates answers through the
pure AnswerValidator/DictationAnalyzer, escalates aid over 3 attempts
via AttemptFlow, feeds DifficultyManager so adaptive difficulty is
actually wired in rather than dead code, and records every attempt
through ProgressManager. Every exercise-type scene (multiple_choice,
sentence_correction, dictation) only emits its answer by signal, per
the architecture invariant.

All child-facing text now comes from data/localization/fr.json via
UIText, not hardcoded in scripts or scenes. Getting that right
required extending SchemaValidator to support "additionalProperties"
as a schema (dynamic keys), which also closed a real gap: save.skills
was previously unvalidated against SkillState's actual shape.

16 new headless tests, including two integration tests that instance
exercise_host.tscn directly and drive it by emitting child-scene
signals, stopping short of the final scene transition (which would
tear down the test runner's own tree). Everything that needs a
screen -- layout at different sizes, touch, virtual keyboard, actual
audio playback (no .ogg files exist yet) -- is listed in the new
docs/testing/manual-checklist.md instead of claimed as verified.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

data/localization/fr.json

@@ -0,0 +1,46 @@
+{
+  "profile_select.title": "Choisis ton profil",
+  "profile_select.new_profile_button": "Nouveau profil",
+  "profile_select.delete_button": "Supprimer",
+  "profile_select.delete_confirm_title": "Supprimer ce profil ?",
+  "profile_select.delete_confirm_message": "Cette action efface pour toujours la progression de ce profil.",
+  "profile_select.delete_confirm_yes": "Oui, supprimer",
+  "profile_select.delete_confirm_no": "Non, annuler",
+  "profile_select.empty_state": "Pas encore de profil : crée le premier !",
+  "profile_create.title": "Crée ton profil",
+  "profile_create.name_label": "Comment t'appelles-tu ?",
+  "profile_create.name_placeholder": "Ton prénom ou ton pseudo",
+  "profile_create.level_label": "Tu es en...",
+  "profile_create.level_ce1": "CE1",
+  "profile_create.level_ce2": "CE2",
+  "profile_create.confirm_button": "Commencer l'aventure",
+  "profile_create.cancel_button": "Retour",
+  "profile_create.name_required_error": "Choisis un prénom avant de continuer.",
+  "world_map.title": "La forêt des accords",
+  "world_map.status_decouverte": "À découvrir",
+  "world_map.status_en_acquisition": "En entraînement",
+  "world_map.status_en_consolidation": "En progrès",
+  "world_map.status_acquise": "Réussie",
+  "world_map.status_a_reviser": "À réviser",
+  "mission_intro.start_button": "Commencer la mission",
+  "mission_intro.back_button": "Retour à la carte",
+  "rule_panel.title": "La règle à retenir",
+  "rule_panel.example_label": "Par exemple :",
+  "rule_panel.continue_button": "C'est parti !",
+  "exercise_host.validate_button": "Valider",
+  "exercise_host.continue_button": "Continuer",
+  "exercise_host.finish_mission_button": "Terminer la mission",
+  "feedback_panel.correct_title": "Bravo !",
+  "feedback_panel.incorrect_title": "Pas tout à fait",
+  "feedback_panel.hint_label": "Indice :",
+  "feedback_panel.explanation_label": "Pourquoi ?",
+  "feedback_panel.correction_label": "La bonne réponse :",
+  "sentence_correction.correction_placeholder": "Corrige ce mot",
+  "dictation.instruction_label": "Écris la phrase que tu entends :",
+  "dictation.input_placeholder": "Écris ici...",
+  "dictation.replay_button": "Réécouter",
+  "dictation.provisional_audio_badge": "Voix provisoire",
+  "reward_screen.title": "Mission réussie !",
+  "reward_screen.stars_label": "Étoiles gagnées :",
+  "reward_screen.continue_button": "Retour à la carte"
+}

data/missions/mission_01_pre_des_mots.json

@@ -0,0 +1,9 @@
+{
+  "mission_id": "mission_01_pre_des_mots",
+  "title": "Le pré des petits mots",
+  "narrative_context": "Les lutins du pré n'arrivent plus à accorder leurs mots entre eux. Aide-les à retrouver les bonnes terminaisons pour que leurs phrases retrouvent leur sens !",
+  "rule_id": "regle_accord_adjectif",
+  "exercise_type": "multiple_choice",
+  "map_position": { "x": 0.2, "y": 0.7 },
+  "review_status": "draft"
+}

data/missions/mission_02_pont_des_phrases.json

@@ -0,0 +1,9 @@
+{
+  "mission_id": "mission_02_pont_des_phrases",
+  "title": "Le pont des phrases",
+  "narrative_context": "Un pont de pierres portant chacune un mot s'est abîmé. Repère la pierre fautive et corrige-la pour que les voyageurs puissent traverser en toute sécurité.",
+  "rule_id": "regle_accord_adjectif",
+  "exercise_type": "sentence_correction",
+  "map_position": { "x": 0.5, "y": 0.4 },
+  "review_status": "draft"
+}

data/missions/mission_03_clairiere_echo.json

@@ -0,0 +1,9 @@
+{
+  "mission_id": "mission_03_clairiere_echo",
+  "title": "La clairière de l'écho",
+  "narrative_context": "L'écho de la clairière répète fidèlement les phrases qu'on lui confie, mais seulement si elles sont bien écrites. Dicte-lui la phrase sans faute pour l'entendre résonner.",
+  "rule_id": "regle_accord_adjectif",
+  "exercise_type": "dictation",
+  "map_position": { "x": 0.8, "y": 0.65 },
+  "review_status": "draft"
+}

data/schemas/localization.schema.json

@@ -0,0 +1,4 @@
+{
+  "type": "object",
+  "additionalProperties": { "type": "string", "minLength": 1 }
+}

data/schemas/mission.schema.json

@@ -0,0 +1,33 @@
+{
+  "type": "object",
+  "required": [
+    "mission_id",
+    "title",
+    "narrative_context",
+    "rule_id",
+    "exercise_type",
+    "map_position",
+    "review_status"
+  ],
+  "additionalProperties": false,
+  "properties": {
+    "mission_id": { "type": "string", "pattern": "^[a-z][a-z0-9_]*$" },
+    "title": { "type": "string", "minLength": 1 },
+    "narrative_context": { "type": "string", "minLength": 1 },
+    "rule_id": { "type": "string", "pattern": "^[a-z][a-z0-9_]*$" },
+    "exercise_type": {
+      "type": "string",
+      "enum": ["multiple_choice", "sentence_correction", "dictation"]
+    },
+    "map_position": {
+      "type": "object",
+      "required": ["x", "y"],
+      "additionalProperties": false,
+      "properties": {
+        "x": { "type": "number", "minimum": 0, "maximum": 1 },
+        "y": { "type": "number", "minimum": 0, "maximum": 1 }
+      }
+    },
+    "review_status": { "type": "string", "enum": ["draft", "validated"] }
+  }
+}

data/schemas/save.schema.json

@@ -18,7 +18,36 @@
     "school_level": { "type": "string", "enum": ["CE1", "CE2"] },
     "session_count": { "type": "integer", "minimum": 0 },
     "unlocked_regions": { "type": "array", "items": { "type": "string" } },
-    "skills": { "type": "object" },
+    "skills": {
+      "type": "object",
+      "additionalProperties": {
+        "type": "object",
+        "required": [
+          "status",
+          "recent_results",
+          "recent_hint_used",
+          "sessions_succeeded",
+          "formats_succeeded",
+          "last_session_practiced",
+          "review_interval_index",
+          "next_review_session"
+        ],
+        "additionalProperties": false,
+        "properties": {
+          "status": {
+            "type": "string",
+            "enum": ["decouverte", "en_acquisition", "en_consolidation", "acquise", "a_reviser"]
+          },
+          "recent_results": { "type": "array", "items": { "type": "boolean" } },
+          "recent_hint_used": { "type": "array", "items": { "type": "boolean" } },
+          "sessions_succeeded": { "type": "array", "items": { "type": "integer" } },
+          "formats_succeeded": { "type": "array", "items": { "type": "string" } },
+          "last_session_practiced": { "type": "integer" },
+          "review_interval_index": { "type": "integer" },
+          "next_review_session": { "type": "integer" }
+        }
+      }
+    },
     "rewards": {
       "type": "object",
       "required": ["stars", "items"],