A repository's map draws only open issues by default, and a "Show done" link draws the rest: trevato/forge's /map under 400 KB #6174

Replaces #6121. Measured 2026-10-26: /trevato/forge/map sends 3.6 MB and spends map;dur≈2240 because it draws 1,969 done issues next to about 370 open ones. main already splits the page's Server-Timing (#5785), and /og/map already draws open issues only, so this issue covers only the page.

Done when:

• [ ] /:owner/:name/map lays out and draws only open issues by default. Ready now, Blocked on, the critical path, marks, counts and pillar rows are still computed on the whole graph, so a closed blocker still frees what it held.
• [ ] The counts line keeps done N as a plain <span class="badge">. A separate padded link beside it reads "Show done" (→ ?done=1), or "Open only" on ?done=1 (→ /map). It is at least 44px tall under pointer: coarse and its class is named in docs/design/areas/map.md. The link appears only when N > 0.
• [ ] The layout cache keys on the filter. The live region refetches the current URL, so ?done=1 keeps its filter.
• [ ] docs/PLANNING.md and the README's Map entry describe the default and ?done=1.
• [ ] test/map-page.test.ts builds 2,000 closed and 300 open issues. It asserts no closed node on the default page, that the body is under 400 KB, both links, and that ?done=1 draws the closed nodes. bun scripts/design-lint.ts passes.

Files: src/web/pages/map.ts, test/map-page.test.ts, docs/PLANNING.md, docs/design/areas/map.md, README.md. Starting point: branch scout/6121-a-repository-s-map-draws-what-is-open-an (pull #6132, closed) has most of this. Re-cut it onto main and keep it to the page. Risk: the toggle is a link, not a badge (docs/design/areas/toolbar.md).