test(backend): cover step 17 modules and extract stubs

Add tests for partnership workflow, middleman adaptation and idea notifications; extract reusable test stubs into separate files; add architecture guard forbidding object-valued dictionaries in data contracts.

tests/TarninaHub.Tests/Controllers/ApplicationsControllerTests.cs

@@ -49,7 +49,7 @@ public class ApplicationsControllerTests
             "application:new",
             "grant_call:x",
             "idea:y",
-            new Dictionary<string, object?>(),
+            new Dictionary<string, string?>(),
             "draft",
             DateTimeOffset.UtcNow);
         var service = new StubApplicationService(
@@ -62,26 +62,4 @@ public class ApplicationsControllerTests
 
         Assert.IsType<CreatedAtActionResult>(result.Result);
     }
-
-    private sealed class StubApplicationService : IApplicationService
-    {
-        private readonly CreateApplicationResult _createResult;
-
-        public StubApplicationService(CreateApplicationResult createResult)
-        {
-            _createResult = createResult;
-        }
-
-        public Task<CreateApplicationResult> CreateAsync(
-            string userId,
-            CreateApplicationRequest request,
-            CancellationToken cancellationToken) => Task.FromResult(_createResult);
-
-        public Task<ApplicationResponse?> GetAsync(string applicationId, CancellationToken cancellationToken) =>
-            Task.FromResult(_createResult.Application);
-
-        public Task<IReadOnlyList<ApplicationResponse>> ListForAuthorAsync(
-            string authorId,
-            CancellationToken cancellationToken) => Task.FromResult<IReadOnlyList<ApplicationResponse>>([]);
-    }
 }