feat: 实现考试分数智能分配

解决题目数量无法整除总分时出现无限小数的问题

后端：
- 新增 ScoreDistributor 分数分配工具类
- 支持整数分配和小数分配两种模式
- 更新 exam_service.py 使用智能分配
- 考试总分固定100分，按题目数量智能分配

前端：
- 新增 scoreFormatter.ts 分数格式化工具
- 提供分数显示、等级判断等辅助函数

示例：100分/6题 = [17,17,17,17,16,16] 总和=100

backend/app/services/exam_service.py

@@ -11,6 +11,7 @@ from app.models.exam import Exam, Question, ExamResult
 from app.models.exam_mistake import ExamMistake
 from app.models.course import Course, KnowledgePoint
 from app.core.exceptions import BusinessException, ErrorCode
+from app.utils.score_distributor import ScoreDistributor
 
 
 class ExamService:
@@ -54,27 +55,38 @@ class ExamService:
             all_questions, min(question_count, len(all_questions))
         )
 
-        # 构建题目数据
+        # 使用智能分数分配器，确保总分为整数且分配合理
+        total_score = 100.0  # 固定总分为100分
+        actual_question_count = len(selected_questions)
+        
+        # 创建分数分配器
+        distributor = ScoreDistributor(total_score, actual_question_count)
+        distributed_scores = distributor.distribute(mode="integer")
+
+        # 构建题目数据，使用分配后的分数
         questions_data = []
-        for q in selected_questions:
+        for i, q in enumerate(selected_questions):
             question_data = {
                 "id": str(q.id),
                 "type": q.question_type,
                 "title": q.title,
                 "content": q.content,
                 "options": q.options,
-                "score": q.score,
+                "score": distributed_scores[i],  # 使用智能分配的分数
             }
             questions_data.append(question_data)
 
+        # 计算及格分数（向上取整，确保公平）
+        pass_score = ScoreDistributor.calculate_pass_score(total_score, 0.6)
+
         # 创建考试记录
         exam = Exam(
             user_id=user_id,
             course_id=course_id,
             exam_name=f"{course.name} - 随机测试",
-            question_count=len(selected_questions),
-            total_score=sum(q.score for q in selected_questions),
-            pass_score=sum(q.score for q in selected_questions) * 0.6,
+            question_count=actual_question_count,
+            total_score=total_score,
+            pass_score=pass_score,
             duration_minutes=60,
             status="started",
             questions={"questions": questions_data},
@@ -140,6 +152,9 @@ class ExamService:
         for question_data in exam.questions["questions"]:
             question_id = question_data["id"]
             question = questions_map.get(question_id)
+            
+            # 使用考试创建时分配的分数（智能分配后的整数分数）
+            allocated_score = question_data.get("score", 10.0)
 
             if not question:
                 continue
@@ -148,7 +163,7 @@ class ExamService:
             is_correct = user_answer == question.correct_answer
 
             if is_correct:
-                total_score += question.score
+                total_score += allocated_score  # 使用分配的分数
                 correct_count += 1
 
             # 创建答题结果记录
@@ -157,7 +172,7 @@ class ExamService:
                 question_id=int(question_id),
                 user_answer=user_answer,
                 is_correct=is_correct,
-                score=question.score if is_correct else 0.0,
+                score=allocated_score if is_correct else 0.0,  # 使用分配的分数
             )
             db.add(exam_result)