Fix build errors and enable TreatWarningsAsErrors across all projects

Remove duplicate source files from old ApiKeys/, Authentication/, and
Authorization/ folders that were already migrated to Common/Security/.
Update test namespace usings to match. Pin EFC Relational 10.0.5 to
resolve MSB3277 version conflict with Npgsql's transitive dependency.
Add LangVersion and TreatWarningsAsErrors to AppHost and ServiceDefaults.

tests/api/MicCheck.Api.Tests.Unit/Authorization/TokenServiceTests.cs

@@ -1,5 +1,5 @@
 using System.IdentityModel.Tokens.Jwt;
-using MicCheck.Api.Authorization;
+using MicCheck.Api.Common.Security.Authorization;
 using MicCheck.Api.Organizations;
 using MicCheck.Api.Users;
 using Microsoft.Extensions.Configuration;