docs: recapture the four README screenshots after the SPA revamp slices land #920

Part of #674. Filed by the owner (2026-09-21) as the last slice of the revamp: the four README screenshots still show the pre-revamp SPA, and they should be recaptured once, at the end, rather than churned after each slice.

What is stale

README.md embeds four committed images, all captured 2026-09-14 against the old CSS SPA:

Every one of them also carries the old shell: the pre-MUI sidebar, headings and controls that #833 (#901, merged) replaced with the Field Console treatment — warm-paper surfaces, serif h1/h2, rectangular actions.

Do this after the revamp lands

Blocked on the SPA revamp slices that change these screens or the shell: #831, #908, #914, #915, #916, #828, #835, #836 (and #824/#825, which change no pixels but gate the guards). Start only when they are merged.

• Rebuild the simulation stack at main (tools/simulation/reset.sh), then cd tools/simulation/ui && npm run screenshots. The spec writes all four files into docs/images/ at 1:1 (AGENTS.md: three conventions earned while shipping #651 + #652 #662); the dashboard and sales captures use the demo-seeded readme-farm (feat(sim): seed a second farm for the README dashboard capture #867), daily entry and reports use the simulation farm.
• Commit the four regenerated PNGs. These are the repo's own tracked images, the deliberate exception to "attach, never commit" (docs/images/dashboard.png is generated by the screenshot spec but never committed #663).
• Update the alt text and the surrounding prose in README.md. The current alt text describes controls the redesign moved or renamed (for example the sales list's "history column naming the user who created and confirmed each order"). Read each new capture and describe what it actually shows.
• Check tools/simulation/ui/specs-screenshots/screenshots.spec.ts still selects the right regions: the redesigned screens changed DOM structure, so a selector or scroll target may capture the wrong band even when the run is green.
• If the palette/theme captures under npm run palettes (SPA: visual check of #651/#652 in night mode and the three non-default farm palettes #664) are also stale, refresh them in the same pass.

Depends on, but is not blocked by

#886 (PR #917) gives the demo farm fourteen complete days, so the dashboard's fortnight strip stops rendering half hatched. If that has merged first, the new capture picks it up automatically; if not, note in the PR which strip state the capture shows.

Done when

The four images in docs/images/ show the current SPA, their alt text matches what they show, and the README prose names no control the revamp removed.