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/tests/fixtures/hooks.ts

@@ -53,6 +53,8 @@ export function makeWorkspaceContextValue(
     personalDataUuid: parent.uuid,
     parentName: parent.name,
     refreshContext: vi.fn(),
+    planVersion: 0,
+    bumpPlanVersion: vi.fn(),
     ...overrides,
   }
 }
@@ -127,6 +129,7 @@ export function makeScraperFetchResult(
     cancel: vi.fn(),
     isRunning: false,
     isTerminal: false,
+    partnerDeduction: null,
     ...overrides,
   }
 }