ikhal: New alarm fields should default to empty

In ikhal, when adding a new alarm in a new event ("n" -> alarms -> add), the fields are pre-populated with zeros, which means I always need to erase it to enter a single digit number, since switching to the field and just typing "1" will turn it into 10 instead. This always felt incredibly weird for me. I guess that the problem is that the field lacks "pre-selection" normally enabled on default fields that would cause the exiting text to be replaced by default.

I believe a better option would be to leave all fields blank, and eventually fill them with zeros (if needed?) when the form is saved.

Overall even the date/time fields behave similarly weird. I'd almost expect overwrite behavior on those. Maybe we can switch to the thin cursor to make it more obvious?

Start by reproducing the issue in ikhal with a new event using "n" → alarms → add, then locate the alarm form entry point and inspect how its fields are initialized. Done means newly added alarm fields start blank and can accept a single digit without first erasing a zero; confirm the behavior when saving the form.