refactor(core): delegate TaskRowDto.to_dict to model_dump(mode="json") (#1105)

The hand-written to_dict mapped all 20 fields one by one, duplicating
exactly what Pydantic's model_dump(mode="json") already produces: enums to
their .value, datetimes/date keys to ISO strings, primitives untouched.
Verified byte-for-byte equal (keys and values) on a fully populated row, and
the exporter/presenter suites (105 tests) that consume it still pass.

Net -27 LOC, no behavior change.

Author: Kohei-Wada

packages/taskdog-core/src/taskdog_core/application/dto/task_dto.py

@@ -127,34 +127,7 @@ def to_dict(self) -> dict[str, object]:
         Returns:
             Dictionary with all task fields, using string values for enums and ISO format for datetimes.
         """
-        return {
-            "id": self.id,
-            "name": self.name,
-            "priority": self.priority,
-            "status": self.status.value,
-            "planned_start": self.planned_start.isoformat()
-            if self.planned_start
-            else None,
-            "planned_end": self.planned_end.isoformat() if self.planned_end else None,
-            "deadline": self.deadline.isoformat() if self.deadline else None,
-            "actual_start": self.actual_start.isoformat()
-            if self.actual_start
-            else None,
-            "actual_end": self.actual_end.isoformat() if self.actual_end else None,
-            "estimated_duration": self.estimated_duration,
-            "actual_duration_hours": self.actual_duration_hours,
-            "is_fixed": self.is_fixed,
-            "depends_on": self.depends_on,
-            "tags": self.tags,
-            "daily_allocations": {
-                k.isoformat(): v for k, v in self.daily_allocations.items()
-            },
-            "is_archived": self.is_archived,
-            "is_finished": self.is_finished,
-            "created_at": self.created_at.isoformat(),
-            "updated_at": self.updated_at.isoformat(),
-            "has_notes": self.has_notes,
-        }
+        return self.model_dump(mode="json")
 
 
 class TaskDetailDto(BaseModel):