Let a household choose to be paid for the red days

Asking for a full week off never spent anything on the Saturday, the
Sunday or a holiday, and a test now says so outright rather than leaving
it to be rediscovered. Those days are free because vacation cannot be
taken on a day that is not a working day.

Parental benefit is a payment rather than a schedule, though, so it can
be drawn on a red day to turn an unpaid day off into a paid one — at the
cost of a day the family would otherwise keep. That is now a workspace
setting, off by default, and it never reaches for a vacation day. With it
off the planner behaves exactly as before.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ei7gCZzdd751uZtPzb1Pep

frontend/src/i18n/en/settings.ts

@@ -112,6 +112,9 @@ export const settings = {
   'settings.saveVacationSuccess': 'Vacation days for {year} saved!',
   'settings.selectedChildLabel': 'Selected child:',
   'settings.showWeekNumbers': 'Show week numbers',
+  'settings.takePlOnRedDays': 'Take parental leave on red days',
+  'settings.takePlOnRedDaysError': 'Could not save the setting',
+  'settings.takePlOnRedDaysHelp': 'You get paid for Saturdays, Sundays and red days in the plan — but you spend days you would otherwise have kept, since vacation cannot be taken on these days.',
   'settings.title': 'Settings',
   'settings.vacationHelp': 'Enter vacation days per year. In the first year you are usually home more and have fewer days to spend on vacation, while later years have your full annual allotment. This controls how much time the planner has to work with.',
   'settings.vacationSectionTitle': 'Vacation days',