feat: make roadmap status reports theorem-first

[kim-em]

Voyager's new results posts are readable because they are selective and theorem-first: small semantic sections, one mathematical idea per entry, plain-language significance before implementation names, references at the end, and a compact footer.

This change applies that presentation contract to generated roadmap status snapshots:

• STATUS.md opens with an at-a-glance summary and selectively groups named results, notable definitions/infrastructure, roadmap coverage, and the nearest frontier;
• named results and infrastructure are explicitly capped, and the whole snapshot targets 750 words with a 900-word validator backstop;
• declaration inventories, per-layer mini-essays, and process narrative are explicitly excluded;
• Zulip progress announcements now link both the full PROGRESS.md and current STATUS.md;
• completed roadmaps retain correct /Completed/<area>/... links rather than being sent to the active-roadmap path.

Verification:

• python3 -m compileall -q progress tests
• ./tests/run — all suites passed
• workflow YAML parsed successfully
• active- and completed-roadmap announcement links covered by regression tests