Redesign the setup flow and consolidate the CSS into one primitives layer

Onboarding asks explicitly for one or two parents and shows one card per
parent for balances; the balance form is per parent with inline
validation; the partner can be filled from the FK deduction or added
from it. Settings and Dashboard reuse the same form.

CSS: bare buttons carry no colour any more; buttons, cards, choice
cards, fields, alerts, badges, eyebrow and modal chrome are defined once
in primitives.css. Media queries live only in responsive.css. A style
guard test blocks hex, !important and stray media queries. Bilingual
fixes: calendar selects size by content, header no longer wraps. Vitest
is capped at four workers.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

frontend/src/i18n/sv/calendar.ts

@@ -9,7 +9,7 @@ export const calendar = {
   'calendar.legendKlamdag': 'Klämdag',
   'calendar.legendMinimumRate': 'Lägstanivå',
   'calendar.legendOverride': 'Undantag (arbets-/ledig dag)',
-  'calendar.legendRedDay': 'Röd dag',
+  'calendar.legendRedDay': 'R = röd dag',
   'calendar.legendTitle': 'Teckenförklaring',
   'calendar.legendVacation': 'Semester',
   'calendar.loading': 'Laddar kalender...',
@@ -52,8 +52,6 @@ export const calendar = {
   'plannedDayModal.parentLabel': 'Förälder',
   'plannedDayModal.pinnedNotice': 'Den här dagen är låst av dig — planeraren ändrar den inte automatiskt.',
   'plannedDayModal.dayStatusLabel': 'Den här dagen är:',
-  'plannedDayModal.workdayOption': 'Arbetsdag',
-  'plannedDayModal.dayOffOption': 'Ledig',
   'plannedDayModal.rangeTitle': 'Planera {count} dagar',
   'plannedDayModal.saveButton': 'Spara',
   'plannedDayModal.saveError': 'Det gick inte att spara den planerade dagen',