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/Architecture/NoObjectValuedDictionariesTests.cs

@@ -0,0 +1,60 @@
+using System.Text.RegularExpressions;
+
+namespace TarninaHub.Tests.Architecture;
+
+/// <summary>
+/// Guarantees that data contracts never expose object-valued dictionaries.
+/// Such dictionaries break CBOR deserialization of SurrealDB rows and force
+/// lossy conversions, so only string-valued maps are allowed.
+/// </summary>
+public class NoObjectValuedDictionariesTests
+{
+    private static readonly Regex Forbidden = new(@"Dictionary<string,\s*object", RegexOptions.Compiled);
+
+    [Fact]
+    public void DataContracts_MustNotUseObjectValuedDictionaries()
+    {
+        var root = FindRepositoryRoot();
+        var files = new List<string>();
+
+        foreach (var directory in new[]
+                 {
+                     Path.Combine(root, "backend", "Application", "Dtos"),
+                     Path.Combine(root, "backend", "Application", "Abstractions"),
+                     Path.Combine(root, "backend", "Domain"),
+                 })
+        {
+            files.AddRange(Directory.GetFiles(directory, "*.cs", SearchOption.AllDirectories));
+        }
+
+        files.AddRange(Directory.GetFiles(
+            Path.Combine(root, "backend", "Infrastructure", "Persistence"),
+            "*Row.cs",
+            SearchOption.AllDirectories));
+
+        var offenders = files
+            .Where(file => Forbidden.IsMatch(File.ReadAllText(file)))
+            .Select(file => Path.GetRelativePath(root, file))
+            .OrderBy(path => path, StringComparer.Ordinal)
+            .ToList();
+
+        Assert.True(
+            offenders.Count == 0,
+            "Object-valued dictionaries are forbidden in data contracts. " +
+            "Use string-valued maps instead:\n" + string.Join(Environment.NewLine, offenders));
+    }
+
+    private static string FindRepositoryRoot()
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+
+        while (directory is not null && !File.Exists(Path.Combine(directory.FullName, "TarninaHub.slnx")))
+        {
+            directory = directory.Parent;
+        }
+
+        Assert.NotNull(directory);
+
+        return directory!.FullName;
+    }
+}