Hide + archive stale listings (old jobs, expired shifts)

- ListingPolicy.JobFreshnessDays=30: public /Jobs and home hide jobs older than the cutoff (shifts already require Date>=today)
- ListingArchiver flips stale Open→Expired: shifts past their date, jobs older than the cutoff. Runs at startup and on every IngestionWorker cycle (independent of ingestion being enabled)
- Verified: backdated job dropped off /Jobs (6→5) and was archived to Expired on the sweep

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Pages/Jobs/Index.cshtml.cs

@@ -39,7 +39,8 @@ public class IndexModel : PageModel
             .Include(j => j.Facility).ThenInclude(f => f.City)
             .Include(j => j.Facility).ThenInclude(f => f.District)
             .Include(j => j.Role)
-            .Where(j => j.Status == ShiftStatus.Open);
+            .Where(j => j.Status == ShiftStatus.Open
+                && j.CreatedAt >= JobsMedical.Web.Services.Scraping.ListingPolicy.JobCutoffUtc);
 
         if (CityId is not null) q = q.Where(j => j.Facility.CityId == CityId);
         if (DistrictId is not null) q = q.Where(j => j.Facility.DistrictId == DistrictId);