feat(tasks): add Task CRUD API with 5-state workflow

- TaskService with CRUD operations + state machine enforcement
- 5 DTOs: TaskListDto, TaskDetailDto, CreateTaskRequest, UpdateTaskRequest
- Minimal API endpoints: GET /api/tasks, GET /api/tasks/{id}, POST, PATCH, DELETE
- State machine: Open→Assigned→InProgress→Review→Done (invalid transitions → 422)
- Concurrency: DbUpdateConcurrencyException → 409 Conflict
- Authorization: POST (Manager+), DELETE (Admin), GET/PATCH (Member+)
- RLS: Automatic tenant filtering via TenantDbConnectionInterceptor
- 10 TDD integration tests: CRUD, state transitions, concurrency, role enforcement
- Build: 0 errors (6 BouncyCastle warnings expected)

Task 14 complete. Wave 3: 2/5 tasks done.

backend/WorkClub.Application/Tasks/DTOs/TaskListDto.cs

@@ -0,0 +1,16 @@
+namespace WorkClub.Application.Tasks.DTOs;
+
+public record TaskListDto(
+    List<TaskListItemDto> Items,
+    int Total,
+    int Page,
+    int PageSize
+);
+
+public record TaskListItemDto(
+    Guid Id,
+    string Title,
+    string Status,
+    Guid? AssigneeId,
+    DateTimeOffset CreatedAt
+);