Strip comments and dedupe normalized literals in backend tests

- Remove all // and /// comments from the backend test suite.
- Replace hardcoded normalized-form string literals (e.g. NormalizedTitle/
  NormalizedName duplicating a title/name in upper case) with a variable
  plus .ToUpperInvariant(), so the two values can't drift apart.

backend/Tests/Musify.Api.Tests/TestSupport/FakeAuthenticationHandler.cs

@@ -6,12 +6,6 @@ using Microsoft.Extensions.Options;
 
 namespace Musify.Api.Tests.TestSupport
 {
-    /// <summary>
-    /// Replaces the real JwtBearer handler in the test host: a request carrying the
-    /// <see cref="UserIdHeader"/> header authenticates as that user id, with no real token,
-    /// issuer or JWKS endpoint involved. A request without the header stays anonymous, so
-    /// endpoints under <c>.RequireAuthorization()</c> correctly answer 401.
-    /// </summary>
     public sealed class FakeAuthenticationHandler(
         IOptionsMonitor<AuthenticationSchemeOptions> options,
         ILoggerFactory logger,