**Context**
Fix empty marketplace at /partners/list: page was being statically
prerendered with getPartners() returning [] (build-time fetch failure),
then served from OpenNext's R2 cache forever — so the partners API was
never actually called in production.
**Change**
Wrap getPartners in unstable_cache with revalidate: 300, matching the
existing fetchGithubStarCount / fetchDiscordMemberCount ISR pattern.
After deploy, the cached empty result expires within 5 minutes and the
worker refetches from the partners API at runtime (where the env vars
actually exist), populating the page. Also drops the now-redundant
cache: 'no-store' from partnersApiFetch.
