fix: keep release badges current after docs sync

[hannesrudolph]

What Problem This Solves

Fixes the Releases badge and homepage announcement staying on v2026.9.7 after newer release notes are published.

User Impact

Readers see the newest available stable release and follow its correct release-notes link, including v2026.9.8.

Why This Change Was Made

The badge now follows the synced English release pages instead of a manually pinned version. It uses the selected page's summary and excludes hidden, draft, unreleased and beta pages. Existing localized labels and links are preserved.

Evidence

• All five focused announcement tests pass, including a full build that advances the badge after a newer release page is added.
• Coverage includes numeric version ordering, hidden/draft/beta exclusion, translated links, and behavior after navigation and reload.
• A bounded 30-page preview renders v2026.9.8 in the sidebar and homepage announcement; the sidebar badge was visually checked.
• Independent code review passed. No generated docs, translations, or release-note copy were edited.