Instead of loading all people names and checking each one in memory,
query the database directly for Person items that need refresh:
- Missing primary image OR missing overview
- Not refreshed within the last 30 days
This reduces the operation from N+1 queries (1 for all names + 1 per
person to load) to a single filtered query returning only the IDs that
need work.
Move image refresh logic from PeopleValidator (which runs during library
scans) into PeopleValidationTask (the "Refresh People" scheduled task).
This keeps library scans fast while ensuring the scheduled task fetches
missing images from remote providers like TMDB.
People missing a Primary image or overview get refreshed with
MetadataRefreshMode.Default instead of ValidationOnly, with a 30-day
cooldown to avoid hammering providers for people they have no data for.
Fixes jellyfin#8103
