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/vitest.config.ts

@@ -13,6 +13,17 @@ export default defineConfig({
     globals: true,
     environment: 'jsdom',
     setupFiles: ['./tests/setup.ts'],
+    // Cap the worker pool: unbounded, Vitest forks one jsdom worker per CPU core
+    // (12 on the dev machine) and a coverage run has exhausted the machine's memory
+    // when two runs overlapped. Four workers keeps a run under ~3 GB with little
+    // wall-clock cost; CI runners have fewer cores anyway.
+    pool: 'forks',
+    poolOptions: {
+      forks: {
+        maxForks: 4,
+        minForks: 1,
+      },
+    },
     // The Playwright E2E suite lives under e2e/ and uses @playwright/test's
     // own test runner (`npm run e2e`), not Vitest's — exclude it here so
     // `vitest run` never tries to collect those specs.