Fixes for forms, campaign API filtering, click statistics and the performance chart

If a form contained a preference group created by duplicating another group, the two groups could not be filled in independently ‑ any change to the copy was written back to the original group and vice versa. Preference groups now behave independently in forms regardless of whether they were created by duplication.

The GET /campaigns endpoint returned no results when filtering by the updated_at parameter, because it compared the date for an exact match including time. At the same time, the date_from and date_to filters operated on a column that was not populated for campaigns, so some campaigns were silently missing from the results. Filtering by date now returns the correct campaigns, and the response also includes a created_at field.

Clicking the unsubscribe link in an email from an automation was counted among clicks, which skewed the click rate and made it impossible to accurately evaluate performance. Unsubscribes are no longer counted in click statistics.

The campaign performance chart did not match the actual delivery and open data ‑ the timing of the first events was shifted, and the open counts both per hour and in total were lower than reality. The chart now shows the correct values at the correct time.