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/dictations/cm1_c_est_s_est_dictee_03.json

@@ -0,0 +1,52 @@
+{
+  "id": "cm1_c_est_s_est_dictee_03",
+  "level": "CM1",
+  "domain": "orthographe",
+  "rule_ids": [
+    "regle_c_est_s_est"
+  ],
+  "difficulty": 3,
+  "target_text": "Quand la pluie s'est arrêtée, c'est le soleil qui est revenu.",
+  "words": [
+    {
+      "text": "Quand",
+      "expects_capital": true
+    },
+    {
+      "text": "la"
+    },
+    {
+      "text": "pluie"
+    },
+    {
+      "text": "s'est",
+      "rule_id": "regle_c_est_s_est"
+    },
+    {
+      "text": "arrêtée,"
+    },
+    {
+      "text": "c'est",
+      "rule_id": "regle_c_est_s_est"
+    },
+    {
+      "text": "le"
+    },
+    {
+      "text": "soleil"
+    },
+    {
+      "text": "qui"
+    },
+    {
+      "text": "est"
+    },
+    {
+      "text": "revenu."
+    }
+  ],
+  "audio_id": "cm1_c_est_s_est_dictee_03",
+  "audio_provisional": true,
+  "accepted_variants": [],
+  "review_status": "draft"
+}