Retire the open-ledger card from the homepage

[BrickerP]

Why

open-ledger had no feed: the quant pipeline that published to it was removed on 2026-10-14 (quant-trading #493; its ingest token was never configured), and the public demo ledger holds a single deploy-smoke event while the homepage card says "Every fill hash-chained…". ledger-mcp only serves a built-in synthetic dataset. Both Workers are being retired (profile-repo PR + Cloudflare deletion), so the homepage has to stop linking them first.

Changes

• Remove the Exp. 03 open-ledger card and the ledger-mcp ↗ link in the Also line.
• Renumber: Cookiy becomes Exp. 03, the private entry Exp. 04, the contact title Exp. 05. The private entry spans the grid as a full-width strip so the last row is not half empty.
• src/pens.ts: drop the open-ledger hand and the loop option only it used. Four hands, data-ink 0–3.
• verify-static: four hands / eight seeds, at least seven ruled boxes, Exp. 05, and a guard that the homepage never mentions open-ledger or ledger-mcp again.
• The architecture hub is untouched on purpose. Fig.05 and Fig.06 are dated prints of the quant repo's topology (the PNGs are drawn from a D2 file that lives outside git), and the page has no link to either Worker.

Order of operations

1. Merge Teach the post-deploy smoke test the film poster and video types #96 (the post-deploy smoke test learns jpg/webm/mp4), otherwise the next main deploy job turns red again.
2. Merge this PR.
3. Delete the open-ledger and ledger-mcp Workers on Cloudflare.
4. Merge the profile-repo PR that removes projects/open-ledger, projects/ledger-mcp, their workflows and the profile-cards ledger tile.

[BrickerP]

Superseded by #98, which replaces the open-ledger card with the Agent Stack Index instead of removing it.