Convert Tasks module to MediatR commands/queries

Replaces ITaskService/TaskService, completing the CQRS/mediator
refactor. All 9 old service interfaces are now gone except
IPermissionService, ITokenService, and IPasswordHasher, which stay
plain injected services by design (see spec).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

mws.application/Tasks/Queries/GetTasks.cs

@@ -0,0 +1,21 @@
+using AutoMapper;
+using MediatR;
+using Mws.Application.Common;
+using TaskPriority = Mws.Domain.Tasks.TaskPriority;
+using TaskStatus = Mws.Domain.Tasks.TaskStatus;
+
+namespace Mws.Application.Tasks;
+
+public record GetTasksQuery(Guid UserId, Guid ProjectId, TaskStatus? Status, TaskPriority? Priority, Guid? AssigneeId)
+    : IRequest<List<TaskDto>>;
+
+public class GetTasksHandler(IUnitOfWork uow, IMapper mapper) : IRequestHandler<GetTasksQuery, List<TaskDto>>
+{
+    public async Task<List<TaskDto>> Handle(GetTasksQuery query, CancellationToken ct)
+    {
+        await TaskAccess.EnsureMemberAccessAsync(uow, query.UserId, query.ProjectId, ct);
+
+        var tasks = await uow.Tasks.GetForProjectAsync(query.ProjectId, query.Status, query.Priority, query.AssigneeId, ct);
+        return mapper.Map<List<TaskDto>>(tasks);
+    }
+}