Move the console onto ReUI PRO

Install ReUI (MCP, skill, @reui registry, Tailwind v4, shadcn base-nova) and move
the shared UI onto it: Button, Tag, Check, Input/Textarea, Segmented, Alert, Panel,
Dialog, Tooltip, Menu and Select (Popover), Toast (sonner), the Table frame
(DataGrid), the Dashboard KPI strip, the shnt Ops palette, Geist and the type scale.

Design only: behaviour, texts and roles are unchanged. Tests that asserted the old
DOM were updated; the tests now format numbers in English wherever they run.
docs/reui-migration-plan.md records the plan and its decisions.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

src/ui/useSectionInView.test.tsx

@@ -0,0 +1,57 @@
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { act, render, screen } from '@testing-library/react'
+import { useSectionInView } from './useSectionInView'
+
+afterEach(() => vi.unstubAllGlobals())
+
+/** An IntersectionObserver the test drives by hand. */
+function fakeObserver() {
+  const made: { fire: (ids: [string, boolean][]) => void; observed: string[] }[] = []
+  class Fake {
+    observed: string[] = []
+    constructor(cb: IntersectionObserverCallback) {
+      const fire = (ids: [string, boolean][]) =>
+        cb(
+          ids.map(([id, on]) => ({ target: document.getElementById(id)!, isIntersecting: on }) as unknown as IntersectionObserverEntry),
+          this as unknown as IntersectionObserver,
+        )
+      made.push({ observed: this.observed, fire })
+    }
+    observe(el: Element) { this.observed.push(el.id) }
+    disconnect() {}
+  }
+  vi.stubGlobal('IntersectionObserver', Fake)
+  return made
+}
+
+function Page({ ids }: { ids: string[] }) {
+  const here = useSectionInView(ids)
+  return (
+    <>
+      {ids.map((id) => <div key={id} id={id} />)}
+      <output>{here ?? 'none'}</output>
+    </>
+  )
+}
+
+describe('useSectionInView', () => {
+  it('observes the sections by id and answers the topmost one on screen', () => {
+    const made = fakeObserver()
+    render(<Page ids={['a', 'b', 'c']} />)
+    expect(made[0].observed).toEqual(['a', 'b', 'c'])
+    act(() => made[0].fire([['b', true], ['c', true]]))
+    expect(screen.getByRole('status')).toHaveTextContent('b')
+    act(() => made[0].fire([['b', false]]))
+    expect(screen.getByRole('status')).toHaveTextContent('c')
+  })
+
+  it('a section that left the list is nowhere, and a new array of the same ids observes nothing new', () => {
+    const made = fakeObserver()
+    const { rerender } = render(<Page ids={['a', 'b']} />)
+    act(() => made[0].fire([['a', true]]))
+    rerender(<Page ids={['a', 'b']} />)
+    expect(made).toHaveLength(1)
+    rerender(<Page ids={['x', 'y']} />)
+    expect(screen.getByRole('status')).toHaveTextContent('none')
+  })
+})