Add several boards per level, CM1/CM2 levels and the CE1 'plage des sons' pilot board (0.6.0)

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

data/exercises/ce1/ce1_s_ss_qcm_03.json

@@ -0,0 +1,23 @@
+{
+  "id": "ce1_s_ss_qcm_03",
+  "level": "CE1",
+  "domain": "orthographe",
+  "skill": "sons_et_lettres",
+  "rule_id": "regle_s_ss",
+  "difficulty": 1,
+  "type": "multiple_choice",
+  "instruction": "Choisis le bon mot.",
+  "question": "Ma ... est près de l'école.",
+  "answers": [
+    "maison",
+    "maisson"
+  ],
+  "correct_answer": 0,
+  "hint": "Écoute : tu entends [z], pas [s].",
+  "explanation": "On entend [z] entre deux voyelles : un seul « s », on écrit « maison ».",
+  "review_tags": [
+    "sons_lettres",
+    "s_ss"
+  ],
+  "review_status": "draft"
+}