Keep the closed history open across pages and let readers choose the page size

[ClaudiuSchuster]

What (feel round 2)

1. The closed history stays unfolded: every page turn used to rebuild the list and hand back a fresh, folded <details> — readers had to click "show finished projects" again on every page. The fold now remembers its open state (summary clicks record it; re-renders restore it), search still reaches the closed work directly by auto-opening, and mission changes reset it.

2. Reader-chosen page size: a small "projects per page" selector (6 / 12 / 24 / 48, styled like the filter chips) sits at the end of the filter bar — deliberately outside the pager bars, so the control never disappears when a group happens to fit on one page. Changing it is a preference, not a view: it survives searches, filters and missions, and resets every group to its first page.

Verification

• test-projects-ui.mjs 21/21 (extended: history open across a page turn, page size 24 collapses a group to a single page and back) in podman node:24-slim; check-repository.sh green.
• Local dev-server render (16 seeded projects) in a real browser: manual history open → next page → still open with page-two cards; setting 24 per page puts all 8 open and all 8 closed projects on one page each.