Add CM1 and CM2 boards, six backdrops and a quit button (0.8.0)

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

data/exercises/cm2/cm2_futur_cond_qcm_05.json

@@ -0,0 +1,23 @@
+{
+  "id": "cm2_futur_cond_qcm_05",
+  "level": "CM2",
+  "domain": "grammaire",
+  "skill": "conjugaison_cm2",
+  "rule_id": "regle_futur_conditionnel",
+  "difficulty": 2,
+  "type": "multiple_choice",
+  "instruction": "Choisis le bon mot.",
+  "question": "Quand il fera beau, nous ... en forêt.",
+  "answers": [
+    "irions",
+    "irons"
+  ],
+  "correct_answer": 1,
+  "hint": "Après « quand » + futur, on reste au futur.",
+  "explanation": "Après « quand il fera », on écrit le futur : « irons ».",
+  "review_tags": [
+    "verbes_cm2",
+    "futur_cond"
+  ],
+  "review_status": "draft"
+}