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/utils/members.ts

@@ -0,0 +1,22 @@
+import type { PersonalData } from '@/types'
+
+/** True when `member` is the signed-in user identified by `personalDataUuid`. */
+export function isSelf(member: PersonalData, personalDataUuid: string | null): boolean {
+  return personalDataUuid !== null && member.uuid === personalDataUuid
+}
+
+/**
+ * Stable-sorts `members` so the signed-in user (if present among them) comes
+ * first, leaving every other member in their original relative order.
+ *
+ * Used to put "your" `ParentBalanceForm` ahead of a partner's in any UI that
+ * lists both — see `ParentBalanceForm.tsx`.
+ */
+export function orderSelfFirst(
+  members: PersonalData[],
+  personalDataUuid: string | null,
+): PersonalData[] {
+  const self = members.filter((m) => isSelf(m, personalDataUuid))
+  const others = members.filter((m) => !isSelf(m, personalDataUuid))
+  return [...self, ...others]
+}