Add next_due_date editing to admin task form

- Add NextDueDate field to UpdateTaskRequest DTO
- Add handler logic to process next_due_date updates
- Add next_due_date input field to task edit form
- Update TypeScript models with next_due_date field

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/admin/dto/requests.go

@@ -135,6 +135,7 @@ type UpdateTaskRequest struct {
 	StatusID      *uint    `json:"status_id"`
 	FrequencyID   *uint    `json:"frequency_id"`
 	DueDate       *string  `json:"due_date"`
+	NextDueDate   *string  `json:"next_due_date"`
 	EstimatedCost *float64 `json:"estimated_cost"`
 	ActualCost    *float64 `json:"actual_cost"`
 	ContractorID  *uint    `json:"contractor_id"`

internal/admin/handlers/task_handler.go

@@ -221,6 +221,13 @@ func (h *AdminTaskHandler) Update(c *gin.Context) {
 			updates["due_date"] = dueDate
 		}
 	}
+	if req.NextDueDate != nil {
+		if *req.NextDueDate == "" {
+			updates["next_due_date"] = nil
+		} else if nextDueDate, err := time.Parse("2006-01-02", *req.NextDueDate); err == nil {
+			updates["next_due_date"] = nextDueDate
+		}
+	}
 	if req.EstimatedCost != nil {
 		updates["estimated_cost"] = decimal.NewFromFloat(*req.EstimatedCost)
 	}