feat(manage): 实现部门负责人视角，支持只读查看部门成员项目与任务

部门负责人/部门管理员可通过系统配置开启，选择管理部门后只读查看
本部门及下级部门成员的全部项目和任务。前端自动根据 department_readonly
标记禁用编辑操作，后端统一注入负责人视角上下文控制数据访问边界。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Models/ProjectTask.php

@@ -2258,6 +2258,39 @@ class ProjectTask extends AbstractModel
         return $task;
     }
 
+    /**
+     * 获取任务（含部门负责人只读视角兜底）
+     * @param int $task_id
+     * @param null|bool $archived true:仅限未归档, false:仅限已归档, null:不限制
+     * @param null|bool $trashed true:仅限未删除, false:仅限已删除, null:不限制
+     * @param array $with
+     * @return self
+     */
+    public static function findForDepartmentView($task_id, $archived = true, $trashed = true, $with = [])
+    {
+        $user = User::auth();
+        $departmentView = UserDepartment::ownerViewContext($user, true);
+        if ($departmentView['enabled']) {
+            $builder = self::with($with)->allData()->where('project_tasks.id', intval($task_id));
+            if ($trashed === false) {
+                $builder->onlyTrashed();
+            } elseif ($trashed === null) {
+                $builder->withTrashed();
+            }
+            $task = $builder->first();
+            if (!empty($task) && UserDepartment::isDepartmentReadonlyProject($departmentView, intval($task->project_id))) {
+                if ($archived === true && $task->archived_at != null) {
+                    throw new ApiException('任务已归档', ['task_id' => $task_id]);
+                }
+                if ($archived === false && $task->archived_at == null) {
+                    throw new ApiException('任务未归档', ['task_id' => $task_id]);
+                }
+                return $task;
+            }
+        }
+        return self::userTask($task_id, $archived, $trashed, $with);
+    }
+
     /**
      * 构建指定周期内的未完成任务查询（用于周报/日报等）
      * @param int $userid