Breadcrumbs: visible trail + BreadcrumbList JSON-LD

Add SeoJsonLd.Breadcrumb + Crumb record + _Breadcrumbs partial, and wire a trail
into the Jobs/Shifts list (landing) and detail pages: خانه › استخدام/شیفت › {نقش}
› {شهر|عنوان}. The role crumb links to the role landing page (more internal
links), and Google can show the breadcrumb path in results. Detail pages emit it
alongside the existing JobPosting JSON-LD.

Improvement 5 of the backlog (SEO).

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

src/JobsMedical.Web/Pages/Shared/_Breadcrumbs.cshtml

@@ -0,0 +1,20 @@
+@model IReadOnlyList<JobsMedical.Web.Services.Crumb>
+@* Visible breadcrumb trail. The last crumb is the current page (no link). Pair with the
+   BreadcrumbList JSON-LD (SeoJsonLd.Breadcrumb) emitted in @@section Head. *@
+@if (Model is { Count: > 1 })
+{
+    <nav class="breadcrumbs" aria-label="مسیر">
+        @for (var i = 0; i < Model.Count; i++)
+        {
+            if (i > 0) { <span class="bc-sep" aria-hidden="true">›</span> }
+            @if (!string.IsNullOrEmpty(Model[i].Url) && i < Model.Count - 1)
+            {
+                <a href="@Model[i].Url">@Model[i].Name</a>
+            }
+            else
+            {
+                <span class="bc-current">@Model[i].Name</span>
+            }
+        }
+    </nav>
+}