fix(configuration-database): resolve ConfigurationDatabase-005,006,008,009,010,011 — bounded gRPC columns, split queries, CSV-parse logging, null guards, coverage

src/ScadaLink.ConfigurationDatabase/Repositories/ExternalSystemRepository.cs

@@ -10,7 +10,7 @@ public class ExternalSystemRepository : IExternalSystemRepository
 
     public ExternalSystemRepository(ScadaLinkDbContext context)
     {
-        _context = context;
+        _context = context ?? throw new ArgumentNullException(nameof(context));
     }
 
     public async Task<ExternalSystemDefinition?> GetExternalSystemByIdAsync(int id, CancellationToken cancellationToken = default)