Add 2 dictées for the accords-du-groupe-nominal chapter

Only 1 existed, below the prompt-lancement.md minimum of 3 per
chapter. Adds difficulty 2 (feminine singular) and difficulty 3
(feminine plural, noun and adjective separated by a complement,
mirroring points 18/23). Audio generated with the Piper voice
(make generate-dictation-audio), credited in assets/CREDITS.md.

With this, regle_accord_adjectif now meets prompt-lancement.md's
minimum content volume: 8 multiple-choice, 4 sentence corrections,
3 dictées.

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

data/dictations/ce1_accord_adjectif_dictee_02.json

@@ -0,0 +1,18 @@
+{
+  "id": "ce1_accord_adjectif_dictee_02",
+  "level": "CE1",
+  "domain": "grammaire",
+  "rule_ids": ["regle_accord_adjectif"],
+  "difficulty": 2,
+  "target_text": "La petite chienne dort.",
+  "words": [
+    { "text": "La", "expects_capital": true },
+    { "text": "petite", "rule_id": "regle_accord_adjectif" },
+    { "text": "chienne" },
+    { "text": "dort." }
+  ],
+  "audio_id": "ce1_accord_adjectif_dictee_02",
+  "audio_provisional": true,
+  "accepted_variants": [],
+  "review_status": "draft"
+}

data/dictations/ce1_accord_adjectif_dictee_03.json

@@ -0,0 +1,20 @@
+{
+  "id": "ce1_accord_adjectif_dictee_03",
+  "level": "CE1",
+  "domain": "grammaire",
+  "rule_ids": ["regle_accord_adjectif"],
+  "difficulty": 3,
+  "target_text": "Les fleurs du jardin sont jolies.",
+  "words": [
+    { "text": "Les", "expects_capital": true },
+    { "text": "fleurs" },
+    { "text": "du" },
+    { "text": "jardin" },
+    { "text": "sont" },
+    { "text": "jolies", "rule_id": "regle_accord_adjectif" }
+  ],
+  "audio_id": "ce1_accord_adjectif_dictee_03",
+  "audio_provisional": true,
+  "accepted_variants": [],
+  "review_status": "draft"
+}