IBlogPost porte IsPublished : le endpoint liste ne le lâche plus sur le wire

Le blog API (Yavsc.Blogs/Program.cs) sérialise en System.Text.Json
(.AddControllers() par défaut), et BlogApiController.GetBlogspot retourne
IEnumerable<IBlogPost>. STJ n'émet que les membres du type déclaré
(l'interface), donc IsPublished — qui n'était que sur les classes
concrètes BlogPost / BlogPostDto — était dropped du payload liste.
PostIt lisait alors IsPublished=false pour tout billet, y compris
publiés (cas prod /BlogSpot/Details/13).

Fix : déclarer IsPublished sur IBlogPost. BlogPost et BlogPostDto
l'implémentent déjà. Tests de wire-shape
(IBlogPostWireShapeTests) ajoutés pour verrouiller le contrat au
niveau du boundary.

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

src/Yavsc.Abstract/Blogspot/IBlogPost.cs

@@ -15,5 +15,23 @@ namespace Yavsc.Blogspot
         // BlogPost entity implements this getter by mapping its
         // ApplicationUser navigation to a BlogPostAuthorDto.
         BlogPostAuthorDto? Author { get; }
+
+        /// <summary>
+        /// Whether this post is published. The server derives this
+        /// from the existence of a row in <c>BlogSpotPublication</c>
+        /// and serves it on the wire so clients (PostIt) can render
+        /// the current publication state without a follow-up request.
+        ///
+        /// <para>This MUST be declared on the interface — not just on
+        /// the concrete <c>BlogPost</c> entity / <c>BlogPostDto</c> —
+        /// because the blog API's list endpoint returns
+        /// <c>IEnumerable&lt;IBlogPost&gt;</c>, and the blog API host
+        /// serialises with System.Text.Json, which emits only the
+        /// members of the declared (interface) type. When
+        /// <c>IsPublished</c> lived only on the concrete classes, STJ
+        /// dropped it from the list payload and PostIt read
+        /// <c>false</c> for every post, including published ones.</para>
+        /// </summary>
+        bool IsPublished { get; set; }
     }
 }