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/entity/UserPriorityWeightsEntity.java

@@ -0,0 +1,49 @@
+package com.guo.learningprogresstracker.entity;
+
+import com.baomidou.mybatisplus.annotation.IdType;
+import com.baomidou.mybatisplus.annotation.TableField;
+import com.baomidou.mybatisplus.annotation.TableId;
+import com.baomidou.mybatisplus.annotation.TableName;
+import lombok.Data;
+
+import java.io.Serializable;
+
+/**
+ * 用户自定义的任务优先级维度权重（每用户一行，依赖多租户拦截器隔离）
+ */
+@TableName(value = "user_priority_weights")
+@Data
+public class UserPriorityWeightsEntity extends BaseEntity implements Serializable {
+
+    @TableId(value = "id", type = IdType.AUTO)
+    private Integer id;
+
+    @TableField(value = "urgency_weight")
+    private Double urgencyWeight;
+
+    @TableField(value = "importance_weight")
+    private Double importanceWeight;
+
+    @TableField(value = "content_difficulty_weight")
+    private Double contentDifficultyWeight;
+
+    @TableField(value = "future_value_weight")
+    private Double futureValueWeight;
+
+    @TableField(value = "subjective_priority_weight")
+    private Double subjectivePriorityWeight;
+
+    @TableField(exist = false)
+    private static final long serialVersionUID = 1L;
+
+    /** 系统默认权重 */
+    public static UserPriorityWeightsEntity defaults() {
+        UserPriorityWeightsEntity entity = new UserPriorityWeightsEntity();
+        entity.setUrgencyWeight(0.35);
+        entity.setImportanceWeight(0.25);
+        entity.setContentDifficultyWeight(0.20);
+        entity.setFutureValueWeight(0.10);
+        entity.setSubjectivePriorityWeight(0.10);
+        return entity;
+    }
+}