Talent lifecycle (21-day expiry) + noindex expired job/shift details

- Talent «آماده به کار» now has its own freshness window (21 days, vs 30
  for jobs) since availability goes stale fast; archiver, browse, and home
  use TalentCutoffUtc.
- Expired/filled job openings and past/filled shifts now emit
  robots noindex so Google drops dead listings instead of keeping
  soft-404 pages. (Talent details were already noindex.)

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

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

@@ -60,7 +60,7 @@ public class IndexModel : PageModel
         LatestTalent = await _db.TalentListings
             .Include(t => t.City).Include(t => t.District).Include(t => t.Role)
             .Where(t => t.Status == ShiftStatus.Open
-                && t.CreatedAt >= JobsMedical.Web.Services.Scraping.ListingPolicy.JobCutoffUtc)
+                && t.CreatedAt >= JobsMedical.Web.Services.Scraping.ListingPolicy.TalentCutoffUtc)
             .OrderByDescending(t => t.CreatedAt)
             .Take(3)
             .ToListAsync();