Updates callback path for authentication

Updates the callback path for authentication to a relative path.

This change removes the hardcoded domain from the callback URL,
making the application more flexible and easier to deploy in
different environments.

Source/ProofOfConcept/Program.cs

@@ -53,7 +53,7 @@ builder.Services.AddAuthentication(o =>
     o.SaveTokens = true;
 
     // This must match exactly what you register at Tesla
-    o.CallbackPath = new PathString("https://automatic-parking.app/token-exchange");
+    o.CallbackPath = new PathString("/token-exchange");
     
     // Scopes you actually need
     o.Scope.Clear();