Google for Jobs: only emit JobPosting JSON-LD for a real named employer

JobPosting requires a valid hiringOrganization; emitting «نامشخص / ثبت نشده» (the
placeholder for aggregated ads with no named center) makes Google reject the
posting and can flag invalid structured data across the site. Add
SeoJsonLd.HasRealEmployer and gate the JobPosting/ShiftPosting <script> on it, so
only listings with a genuine employer get marked up (those are the Jobs-eligible
ones anyway).

Improvement 3 of the backlog (SEO).

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

src/JobsMedical.Web/Pages/Shifts/Details.cshtml

@@ -216,6 +216,10 @@
 }
 
 @section Head {
-    @{ var bu = $"{ViewContext.HttpContext.Request.Scheme}://{ViewContext.HttpContext.Request.Host}"; }
-    @Html.Raw("<script type=\"application/ld+json\">" + JobsMedical.Web.Services.SeoJsonLd.ShiftPosting(s, bu) + "</script>")
+    @* Only for a real named employer — Google for Jobs rejects a placeholder hiringOrganization. *@
+    @if (JobsMedical.Web.Services.SeoJsonLd.HasRealEmployer(f))
+    {
+        var bu = $"{ViewContext.HttpContext.Request.Scheme}://{ViewContext.HttpContext.Request.Host}";
+        @Html.Raw("<script type=\"application/ld+json\">" + JobsMedical.Web.Services.SeoJsonLd.ShiftPosting(s, bu) + "</script>")
+    }
 }