fix: Remove IsDevelopment() check for authentication mode configuration

- Allow DevelopmentHeader authentication in all environments when configured
- Fixes 401 Unauthorized errors in Release mode with DevelopmentHeader config
- appsettings.json Authentication.Mode now controls auth regardless of environment

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/KArtSell.Host/Program.cs

@@ -234,8 +234,7 @@ var authenticationBuilder = builder.Services
         options.DefaultChallengeScheme = authenticationScheme;
     });
 
-if (builder.Environment.IsDevelopment()
+if (authenticationMode.Equals("DevelopmentHeader", StringComparison.OrdinalIgnoreCase))
-    && authenticationMode.Equals("DevelopmentHeader", StringComparison.OrdinalIgnoreCase))
 {
     authenticationBuilder.AddScheme<AuthenticationSchemeOptions, DevelopmentHeaderAuthenticationHandler>(
         authenticationScheme,