fix(seo): proper 500 handler + safe JSON-LD escaping

Add UseExceptionHandler(/error) so unhandled exceptions return a
proper HTML 500 instead of a raw response Googlebot was logging as
a server error in Search Console.

Replace manual quote-only escaping in blog JSON-LD with a J() helper
that uses JsonSerializer so newlines, backslashes, and all other
control characters are safely escaped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

DrSousan.Api/Pages/Blog/Post.cshtml

@@ -8,6 +8,8 @@
     var articleType = ViewData["ArticleType"]?.ToString() ?? "MedicalWebPage";
     var pubDate     = post.PublishedAt?.ToString("yyyy-MM-ddTHH:mm:ssZ") ?? "";
     var updDate     = post.UpdatedAt.ToString("yyyy-MM-ddTHH:mm:ssZ");
+    // Escape a string for safe embedding inside a JSON string literal.
+    static string J(string? s) => System.Text.Json.JsonSerializer.Serialize(s ?? "")[1..^1];
 }
 
 @section Head {
@@ -32,13 +34,13 @@
     <script type="application/ld+json">
     {
       "@@context": "https://schema.org",
-      "@@type": "@articleType",
-      "headline": "@post.Title.Replace("\"","\\\"")  ",
-      "description": "@(ViewData["MetaDesc"]?.ToString()?.Replace("\"","\\\""))",
-      "author": { "@@type": "Person", "name": "@post.Author" },
+      "@@type": "@J(articleType)",
+      "headline": "@J(post.Title)",
+      "description": "@J(ViewData["MetaDesc"]?.ToString())",
+      "author": { "@@type": "Person", "name": "@J(post.Author)" },
       "publisher": {
         "@@type": "Organization",
-        "name": "@ViewData["SiteName"]",
+        "name": "@J(ViewData["SiteName"]?.ToString())",
         "url": "@baseUrl"
       },
       "datePublished": "@pubDate",