The baseline operation now accepts a date_offset interval (e.g. "1 year",
"6 months") and applies it to every date when inserting rows, shifting
historical actuals into the target forecast period.
SQL: {date_col} + '{{date_offset}}'::interval)::date at insert time.
Route: defaults to '0 days' if omitted so existing calls are unaffected.
UI: year/month spinners with a live before→after month chip preview so
the projected landing period is visible before submitting.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Instead of re-fetching all forecast data after scale/recode/clone/reference,
the routes now return the inserted rows directly. The frontend uses ag-Grid's
applyTransaction to add only the new rows, eliminating the full reload round-trip.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>