Make the listing purge SEO-standard: archive (not delete) + 410 Gone

Per the project archive-not-delete convention, the in-place purge now sets out-of-scope
and duplicate aggregated jobs/shifts to ShiftStatus.Archived instead of hard-deleting:
- The row is retained for analysis and the change is reversible.
- The listing drops out of every public screen and the sitemap (which filter Status == Open).
- Its detail page now returns 410 Gone (the standard permanent-removal signal) so search
  engines deindex it cleanly, instead of leaving the off-topic page live at 200 or hard-404ing.
Dedupe of job reposts archives the older copies the same way. Coordinate backfill now also
skips non-Open rows. Valid listings are untouched, so IDs/URLs stay stable.

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

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

@@ -133,14 +133,15 @@ public class IndexModel : PageModel
     }
 
     /// <summary>
-    /// In-place cleanup of existing aggregated jobs/shifts: delete only the out-of-scope ones
-    /// (domestic-helper / promotional / spam) per the current validator, plus near-duplicate job
-    /// reposts. Valid listings keep their IDs/URLs. No re-fetch, no AI — runs inline.
+    /// In-place cleanup of existing aggregated jobs/shifts: ARCHIVE (hide, keep the row) only the
+    /// out-of-scope ones (domestic-helper / promotional / spam) per the current validator, plus
+    /// near-duplicate job reposts. Archived pages drop from lists + sitemap and return 410 Gone.
+    /// Valid listings keep their IDs/URLs. Reversible, no re-fetch, no AI — runs inline.
     /// </summary>
     public async Task<IActionResult> OnPostPurgeInvalidAsync()
     {
-        var (removed, deduped) = await _ingest.PurgeInvalidAggregatedAsync();
-        IngestMessage = $"پاک‌سازیِ درجا: {removed} آگهیِ خارج از حوزه (خدمات منزل/تبلیغاتی/اسپم) و {deduped} استخدامِ تکراری حذف شد. سایر آگهی‌ها و شناسه/آدرسشان دست‌نخورده ماند.";
+        var (archived, deduped) = await _ingest.PurgeInvalidAggregatedAsync();
+        IngestMessage = $"بایگانیِ درجا: {archived} آگهیِ خارج از حوزه (خدمات منزل/تبلیغاتی/اسپم) و {deduped} استخدامِ تکراری از سایت پنهان شد (وضعیت «بایگانی»؛ ردیف نگه داشته شد و قابل بازگشت است؛ صفحه‌شان ۴۱۰ Gone می‌دهد). آگهی‌های معتبر و شناسه/آدرسشان دست‌نخورده ماند.";
         return RedirectToPage();
     }