test(blogs): GET /api/v1/blog returns 200 with empty list

First behavioural test for the Yavsc.Blogs API surface. Sends a
GET on the blog index with the X-Test-Role auth bypass and asserts
the response is 200 with an empty JSON array — the in-memory
ApplicationDbContext has no rows, and BlogSpotService.Index returns
an empty enumeration.

While here, fix a routing miss: AddControllers() in the test
fixture was only scanning the test assembly, so BlogApiController
was never registered. Add the Yavsc.Blogs application part
explicitly. Without this, every request to /api/v1/blog came back
as 404 — the same symptom PostIt was seeing in production.

The POST flow lands in the next commit, once BlogApiController is
made to accept JSON (it currently requires multipart/form-data
because of Request.Form.Files).

src/Yavsc.Blogs.Tests/BlogApiTests.cs

@@ -0,0 +1,65 @@
+using System.Net;
+using System.Text.Json;
+
+namespace Yavsc.Blogs.Tests;
+
+/// <summary>
+/// Behavioural tests for <c>BlogApiController</c>. Built on the
+/// <see cref="BlogsWebServerFixture"/> scaffold: in-memory
+/// <c>ApplicationDbContext</c>, real <c>BlogSpotService</c>,
+/// <c>X-Test-Role</c> for the <c>[Authorize("BlogScope")]</c>
+/// attribute.
+/// </summary>
+public sealed class BlogApiTests : IClassFixture<BlogsWebServerFixture>
+{
+    private readonly BlogsWebServerFixture _fixture;
+
+    public BlogApiTests(BlogsWebServerFixture fixture)
+    {
+        _fixture = fixture;
+    }
+
+    /// <summary>The fixture's <c>WebApplication</c> is bound to
+    /// <c>https://localhost:&lt;random&gt;</c> via
+    /// <see cref="WebHostFixture.Addresses"/>. We pick the first
+    /// https URL and append the controller route
+    /// (<c>/api/v1/blog</c>, matching the production
+    /// <c>[Route(APIPrefix + "/blog")]</c>).</summary>
+    private string BlogsUrl =>
+        _fixture.Addresses.First(a => a.StartsWith("https://")) + "/api/v1/blog";
+
+    private HttpClient NewClient()
+    {
+        // The fixture's self-signed certificate is not in the user's
+        // trust store, so we accept anything (same pattern as
+        // Yavsc.Org.Tests' BypassSslValidationHandler).
+        var handler = new HttpClientHandler
+        {
+            ServerCertificateCustomValidationCallback = (_, _, _, _) => true
+        };
+        var http = new HttpClient(handler)
+        {
+            BaseAddress = new Uri(_fixture.Addresses.First(a => a.StartsWith("https://")))
+        };
+        http.DefaultRequestHeaders.Add(TestAuthPolicyProvider.HeaderName, TestAuthPolicyProvider.AdminRole);
+        return http;
+    }
+
+    [Fact]
+    public async Task GetBlogs_returns_200_with_empty_list_when_no_posts()
+    {
+        using var http = NewClient();
+
+        var response = await http.GetAsync("/api/v1/blog");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var body = await response.Content.ReadAsStringAsync();
+        // Empty table → empty JSON array. We compare as a JsonDocument
+        // so a future change in formatting (whitespace, indentation)
+        // doesn't break the assertion.
+        using var doc = JsonDocument.Parse(body);
+        Assert.Equal(JsonValueKind.Array, doc.RootElement.ValueKind);
+        Assert.Equal(0, doc.RootElement.GetArrayLength());
+    }
+}

src/Yavsc.Blogs.Tests/BlogsWebServerFixture.cs

@@ -1,13 +1,10 @@
 using System.Security.Claims;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.FileProviders;
-using Yavsc;
+using Yavsc.Blogs.Controllers;
 using Yavsc.Models;
-using Yavsc.Server.Services;
 using Yavsc.Services;
 using Yavsc.Tests.Shared;
 
@@ -59,9 +56,12 @@ public sealed class BlogsWebServerFixture : WebHostFixture
         // IFileSystemAuthManager).
         builder.Services.AddScoped<BlogSpotService>();
 
-        // The BlogApiController is reached through MVC, so register
-        // MVC + the BlogScope authorization policy.
-        builder.Services.AddControllers();
+        // The BlogApiController is reached through MVC. AddControllers()
+        // by default scans the test assembly only; we explicitly add the
+        // Yavsc.Blogs application part so the controller is discovered
+        // and routed.
+        builder.Services.AddControllers()
+            .AddApplicationPart(typeof(BlogApiController).Assembly);
         builder.Services.AddAuthorization(opt =>
         {
             // Mirror the production "BlogScope" policy: any