The map page has a First button on each ready issue, and the ranked one shows first

Part of #7640; third slice of #7657. Two taps from the feed: map, First.

Done when:

[ ] A writer sees a First button (a same-origin POST form, no JavaScript needed) on each ready issue on the map page; readers do not
[ ] After it, the page lists that issue first in ready and marks it "first, by <who>"
[ ] bun scripts/design-lint.ts passes; any new class is named in docs/design/areas/map.md
[ ] A test posts the form and finds the order changed; a cross-origin post is refused

Files: src/web/pages/map.ts, docs/design/areas/map.md, test/map-first-page.test.ts

Fits: a builder

The map page has a First button on each ready issue, and the ranked one shows first #7808