fix(form): style the Start-in radios as radios, not checkboxes #100

Follow-up to #88.

Problem #

The Start-in radios (Dry run / Live) reuse the form's checkbox style. That style draws a checkmark with &:checked::after, so the selected radio shows a tick in a square-looking box. A pair of exclusive options looks like two independent checkboxes.

Evidence #

• app/islands/AutomationForm.css.ts:94: the checkbox style and its &:checked::after checkmark, applied to the Start-in radios.

Expected #

The radios look like radios: round, with a filled dot when selected, using the design tokens the checkbox style uses.

Acceptance criteria #

• The Start-in inputs use a radio style with no checkmark.
• Checked, unchecked, focused and disabled states are checked in both themes.

Out of scope #

Restyling other checkboxes in the form.