feat(优先级)：维度权重可配置并即时重算

- 新表 user_priority_weights（每用户一行，默认 0.35/0.25/0.20/0.10/0.10）
- PriorityWeightsService：读取/保存权重，权重和必须为 1，保存后重算全部任务
- TaskController：GET/PUT /tasks/priority-weights
- CalculatedPriorityTool 支持自定义权重
- 修复 updateTask 不重算优先级的问题

src/main/java/com/guo/learningprogresstracker/mapper/UserPriorityWeightsMapper.java

@@ -0,0 +1,9 @@
+package com.guo.learningprogresstracker.mapper;
+
+import com.baomidou.mybatisplus.core.mapper.BaseMapper;
+import com.guo.learningprogresstracker.entity.UserPriorityWeightsEntity;
+import org.apache.ibatis.annotations.Mapper;
+
+@Mapper
+public interface UserPriorityWeightsMapper extends BaseMapper<UserPriorityWeightsEntity> {
+}