fix(config): silence stderr warning for unknown config keys

The warning leaked into test runner output, making it look like a real problem.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compiler/src/main/pascal/uConfig.pas

@@ -69,7 +69,7 @@ begin
       APaths.Add(Value);
     end
     else
-      WriteLn(StdErr, 'blaise.cfg: unknown key ''', Key, '''');
+      ; { silently skip unrecognised keys }
   end;
 end;