Fix HttpUtility reference in auth URL builder

Services/YouTubeAuthService.cs

@@ -30,15 +30,20 @@ public class YouTubeAuthService
 
     public string GetAuthorizationUrl(string redirectUri)
     {
-        var parameters = HttpUtility.ParseQueryString(string.Empty);
+        var query = new[]
-        parameters["client_id"] = _clientId;
+        {
-        parameters["redirect_uri"] = redirectUri;
+            ("client_id", _clientId),
-        parameters["response_type"] = "code";
+            ("redirect_uri", redirectUri),
-        parameters["scope"] = Scope;
+            ("response_type", "code"),
-        parameters["access_type"] = "offline";
+            ("scope", Scope),
-        parameters["prompt"] = "consent";
+            ("access_type", "offline"),
+            ("prompt", "consent"),
+        };
 
-        return $"{AuthorizationEndpoint}?{parameters}";
+        var encoded = string.Join("&", query.Select(kv =>
+            $"{Uri.EscapeDataString(kv.Item1)}={Uri.EscapeDataString(kv.Item2)}"));
+
+        return $"{AuthorizationEndpoint}?{encoded}";
     }
 
     public async Task<YouTubeChannel?> ExchangeCodeForToken(string code, string redirectUri)