Implement opal-task Phases 6-8: Complete CLI Implementation

Phase 6: Display and Basic Commands
- Add display.go with colored formatting for tasks, projects, tags
- Implement cmd/root.go with Cobra command structure
- Implement cmd/list.go for listing and filtering tasks
- Implement cmd/add.go with support for regular and recurring tasks
- Implement cmd/done.go with bulk completion and confirmation

Phase 7: Advanced Commands
- Implement cmd/modify.go for updating task attributes
- Implement cmd/delete.go with soft delete confirmation
- Implement cmd/start.go and cmd/stop.go for task timing
- Implement cmd/count.go for counting filtered tasks
- Implement cmd/projects.go and cmd/tags.go for aggregation

Phase 8: Integration and Polish
- Update main.go to use CLI commands
- Add colored output with fatih/color
- Format task lists with proper alignment
- Highlight overdue tasks in red, upcoming in yellow
- Test end-to-end workflow: add, list, done, recurring tasks
- Verify recurrence spawning works correctly

All CLI commands functional and tested!

opal-task/cmd/delete.go

@@ -0,0 +1,51 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+
+	"git.jnss.me/joakim/opal/internal/engine"
+	"github.com/spf13/cobra"
+)
+
+var deleteCmd = &cobra.Command{
+	Use:   "delete [filter...]",
+	Short: "Delete tasks",
+	Run: func(cmd *cobra.Command, args []string) {
+		if err := deleteTasks(args); err != nil {
+			fmt.Fprintf(os.Stderr, "Error: %v\n", err)
+			os.Exit(1)
+		}
+	},
+}
+
+func deleteTasks(args []string) error {
+	filter, err := engine.ParseFilter(args)
+	if err != nil {
+		return err
+	}
+
+	tasks, err := engine.GetTasks(filter)
+	if err != nil {
+		return err
+	}
+
+	if len(tasks) == 0 {
+		fmt.Println("No tasks matched.")
+		return nil
+	}
+
+	fmt.Printf("Delete %d task(s)? (y/N): ", len(tasks))
+	var confirm string
+	fmt.Scanln(&confirm)
+	if confirm != "y" && confirm != "Y" {
+		return nil
+	}
+
+	for _, task := range tasks {
+		task.Delete(false) // Soft delete
+	}
+
+	fmt.Printf("Deleted %d task(s).\n", len(tasks))
+	return nil
+}