Checklists snap to a proper grid

A small alignment pass on the checklist inside each todo, ruled on by our design committee:

• The dashed "add an item" circle is the same size as the checkboxes above it, so it now sits exactly in their column — it reads as the ghost of your next item, and its label lines up with your item text.
• Archived todos keep the same grid: their checklists no longer shift left when the drag handles disappear.
• The due-date chip stays anchored to the card edge with the title and notes boxes — two clean columns instead of three near-misses.