Each category button now displays "X € restants" below the name,
alongside the existing progress gauge and percentage — so the user
sees both how much of the budget is used and how much is left
without leaving the entry form. Remaining is floored at 0 to match
the gauge's 100% cap.
categoryProgress now returns a ['pct', 'remaining'] pair per category
instead of a bare percentage; tests updated accordingly.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
