Get Facts

Return the current fact set + a cache-hint envelope.

Response shape::

{
  "version": "1.0.0",           # bump when facts change
  "generated_at": "...",        # server render time (UTC)
  "recommended_cache_seconds": 604800,  # 7 days
  "count": 30,
  "facts": [{"text": "...", "category": "..."}, ...]
}

The frontend should stash this in localStorage and only refetch when either (a) version has changed or (b) recommended_cache_seconds has elapsed. The endpoint itself is cheap; the caching is about keeping the loading UX zero-round-trip after first visit.