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/Shifts/Details.cshtml

@@ -5,6 +5,9 @@
     var f = s.Facility!;
     ViewData["Title"] = $"شیفت {s.SpecialtyRequired} - {f.Name}";
     ViewData["Description"] = $"شیفت {s.SpecialtyRequired} در {f.Name}، {f.City?.Name}، تاریخ {JalaliDate.ToLongDate(s.Date)} از ساعت {JalaliDate.Time(s.StartTime)}.";
+    // Past/filled shifts shouldn't stay in the index as dead pages.
+    if (s.Status != JobsMedical.Web.Models.ShiftStatus.Open || s.Date < DateOnly.FromDateTime(DateTime.UtcNow))
+        ViewData["NoIndex"] = true;
     var (badgeClass, typeLabel) = s.ShiftType switch
     {
         ShiftType.Day => ("badge-day", "شیفت صبح"),