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/e2e/support/calendarNav.ts

@@ -36,12 +36,31 @@ export function calendarDayCell(page: Page, isoDate: string) {
  * cells entirely, which reads as a click on the anchor date. Moving in
  * several steps per cell, with a short pause between cells, is what
  * reliably fires a `pointerenter` on each one.
+ *
+ * The whole dragged range is scrolled into view ONCE, before the drag
+ * starts — never mid-drag. A default-viewport (1280×720) run of a 6-row
+ * month puts the trailing week's cells below the fold (`getBoundingClientRect`
+ * still reports their real, off-screen `y`); moving the mouse to those
+ * coordinates without scrolling first sends it past the bottom of the
+ * actually-rendered viewport, where there is no element to receive
+ * `pointerenter` at all — the browser just stops delivering the event, and
+ * the drag's `dragCurrent` freezes on the last on-screen cell it entered
+ * while still climbing toward the target. Scrolling once up front (via the
+ * last, typically lowest, target date) keeps every waypoint's precomputed
+ * center valid for the whole gesture; scrolling again after `mouse.down()`
+ * would invalidate the coordinates of any cell already computed and risk
+ * disrupting the in-progress native pointer sequence.
  */
 export async function dragSelectDates(page: Page, isoDates: string[]): Promise<void> {
   if (isoDates.length < 2) {
     throw new Error('dragSelectDates needs at least two dates to actually drag across')
   }
 
+  const lastDate = isoDates[isoDates.length - 1]
+  if (lastDate) {
+    await calendarDayCell(page, lastDate).scrollIntoViewIfNeeded()
+  }
+
   const centerOf = async (isoDate: string): Promise<{ x: number; y: number }> => {
     const box = await calendarDayCell(page, isoDate).boundingBox()
     if (!box) throw new Error(`calendar day cell not visible for ${isoDate} — is it in the current month view?`)