feat: add course approval history endpoint for instructors to view rejection reasons and approval timeline

Backend/src/types/CoursesInstructor.types.ts

@@ -390,3 +390,31 @@ export interface GetEnrolledStudentDetailResponse {
     data: EnrolledStudentDetailData;
 }
 
+// Course Approval History Types
+export interface ApprovalHistoryItem {
+    id: number;
+    action: string;
+    comment: string | null;
+    created_at: Date;
+    submitter: {
+        id: number;
+        username: string;
+        email: string;
+    } | null;
+    reviewer: {
+        id: number;
+        username: string;
+        email: string;
+    } | null;
+}
+
+export interface GetCourseApprovalHistoryResponse {
+    code: number;
+    message: string;
+    data: {
+        course_id: number;
+        course_title: { th: string; en: string };
+        current_status: string;
+        approval_history: ApprovalHistoryItem[];
+    };
+}