custom reports now warn you about weak or empty results

custom reports now show a warning above the report card when a result looks incomplete or unreliable. warnings appear for fewer than 20 observations, a column with no values, or an outcome rate of exactly 0% or 100%.

warnings are listed by severity and never stop the run. they help you judge how much weight the historical data can carry before you save the report.

when a report runs but produces no numbers at all, the save button is hidden and the builder asks you to describe what the report should calculate. a report that ran and found zero matching sessions can still be saved, since that is a real result. the same checks run on new builds and reruns.