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/components/inputs/DayOverridesInput.tsx

@@ -84,7 +84,7 @@ export function DayOverridesInput({
                   type="button"
                   onClick={() => handleRemove(override.id)}
                   disabled={isSubmitting || isLoading}
-                  className="day-overrides-input__remove-button"
+                  className="btn btn--danger btn--sm btn--block"
                   data-testid={`remove-override-${override.id}`}
                 >
                   {t('common.delete')}
@@ -98,8 +98,10 @@ export function DayOverridesInput({
       <form onSubmit={handleAddOverride} className="day-overrides-input__form" data-testid="add-override-form">
         <h3>{t('dayOverridesInput.addSectionTitle')}</h3>
 
-        <div className="day-overrides-input__form-group">
-          <label htmlFor="override-date">{t('dayOverridesInput.dateLabel')}</label>
+        <div className="field day-overrides-input__form-group">
+          <label htmlFor="override-date" className="field__label">
+            {t('dayOverridesInput.dateLabel')}
+          </label>
           <input
             id="override-date"
             type="date"
@@ -108,7 +110,7 @@ export function DayOverridesInput({
             required
             disabled={isSubmitting || isLoading}
             data-testid="override-date-input"
-            className="day-overrides-input__form-input"
+            className="field__control"
           />
         </div>
 
@@ -142,8 +144,10 @@ export function DayOverridesInput({
           </fieldset>
         </div>
 
-        <div className="day-overrides-input__form-group">
-          <label htmlFor="override-note">{t('dayOverridesInput.noteFieldLabel')}</label>
+        <div className="field day-overrides-input__form-group">
+          <label htmlFor="override-note" className="field__label">
+            {t('dayOverridesInput.noteFieldLabel')}
+          </label>
           <input
             id="override-note"
             type="text"
@@ -153,7 +157,7 @@ export function DayOverridesInput({
             maxLength={280}
             disabled={isSubmitting || isLoading}
             data-testid="override-note-input"
-            className="day-overrides-input__form-input"
+            className="field__control"
           />
           <small className="day-overrides-input__char-count">
             {t('dayOverridesInput.charCount', { count: note.length })}
@@ -163,7 +167,7 @@ export function DayOverridesInput({
         <button
           type="submit"
           disabled={isSubmitting || isLoading || !date}
-          className="day-overrides-input__submit-button"
+          className="btn btn--primary btn--block"
           data-testid="add-override-button"
         >
           {isSubmitting ? t('dayOverridesInput.addingButton') : t('dayOverridesInput.addButton')}