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/common/CalendarDay.tsx

@@ -111,7 +111,20 @@ export function CalendarDay({
       title={title}
       className={className}
       onKeyDown={handleKeyDown}
-      onPointerDown={() => onPointerDown?.(date)}
+      onPointerDown={(e) => {
+        // Touch browsers implicitly capture the pointer to the element it
+        // went down on, so subsequent `pointermove`s never fire
+        // `pointerenter` on the cells the finger drags across — collapsing
+        // a multi-day drag into a single-day tap. Releasing capture
+        // immediately restores normal hover-style `pointerenter` targeting
+        // for the rest of the drag. jsdom (unit tests) doesn't implement
+        // the Pointer Capture API at all, hence the guards.
+        const target = e.currentTarget
+        if (typeof target.hasPointerCapture === 'function' && target.hasPointerCapture(e.pointerId)) {
+          target.releasePointerCapture(e.pointerId)
+        }
+        onPointerDown?.(date)
+      }}
       onPointerEnter={() => onPointerEnter?.(date)}
     >
       <div className="calendar-day__number">{dayNum}</div>