Add @media (max-width: 600px) rule to form.css:
- Stack form row labels above inputs (1fr grid, single column)
- Ensure 44×44px minimum touch targets on checkboxes, radios,
selects, textareas, text inputs, and .btn/.btn--sm
- Stack thesis-add-header and recap-dl grids to single column
- Stack form footer buttons vertically with full width
- Unstick sticky formats fieldset on mobile
- Tighten fieldset margins for narrow viewports