feat(speaking): add grade to TopicDiscussionConfig and SessionConfig types

src/types/englishSpeaking.ts

@@ -50,6 +50,7 @@ export interface LearningGoals {
 // 话题讨论配置
 export interface TopicDiscussionConfig {
   topic: string
+  grade: string
   selectedRole: string
   learningGoals: LearningGoals
   practice: PracticeSettings
@@ -239,6 +240,7 @@ export type SSEEvent =
 // 对话会话配置
 export interface SessionConfig {
   topic: string
+  grade: string
   roleId: string
   totalRounds: number
   vocabulary?: string[]