docs: show the UI in the readme

[ThePrismSystem]

Summary

The readme described the app but never showed it, so the only way to find out what beans-web looks like was to install a Go binary and point it at your projects. Adds three screenshots covering the main tour.

Changes

• Adds a Screenshots section after the intro: the overview, a project's nested bean list, and a bean's detail view
• Ships a light and a dark variant of each behind <picture> + prefers-color-scheme, so the shot matches the theme the reader already has GitHub set to
• Corrects the pnpm version in the prerequisites — the bump to pnpm 11 in chore(deps): apply pending renovate updates #46 left it saying 10

The three shots were picked to show something the prose cannot: that beans nest by parent (a milestone expanding into epics, features and bugs), and that a bean's fields and relationships are editable inline rather than through a form.

Usage

Nothing to use — but the demo data is reproducible rather than hand-made. Screenshots were taken against a throwaway GIT_ROOT seeded with five projects and 42 beans spread across every type, status and priority, with dates spread over eight months so the analytics series has a real shape. No real project data appears in them.

How to validate

The images are worth actually looking at rather than trusting:

1. Open the readme on this branch and confirm all three render, in order, under Screenshots.
2. Flip your GitHub appearance between light and dark (Settings → Appearance) and reload — each screenshot should swap to match. This is the part that silently breaks if a srcset path is wrong, since the <img> fallback still renders.
3. Check the alt text on each by viewing the raw markdown; all three describe the content rather than repeating the caption.

Related links

• chore(deps): apply pending renovate updates #46 — the dependency bump that made the pnpm 10 line stale

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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[codecov]

Bundle Report

Bundle size has no change ✅