feat: improve dialogue speech recognition and AI intervention

kouyu_english/lib/core/models.dart

@@ -111,6 +111,24 @@ class WritingAiFeedback {
   final List<String> missing;
 }
 
+/// Result of AI intervention during a dialogue turn when preset rules do not match.
+class DialogueAiIntervention {
+  const DialogueAiIntervention({
+    required this.accepted,
+    this.suggestion,
+    required this.explanation,
+  });
+
+  /// Whether the learner's response is semantically acceptable for the turn.
+  final bool accepted;
+
+  /// Inferred or corrected English sentence if there was an ASR slip, typo, or minor mistake.
+  final String? suggestion;
+
+  /// Encouraging, concise Chinese explanation of the situation and recommendation.
+  final String explanation;
+}
+
 class AssessmentRecord {
   const AssessmentRecord({
     required this.packId,