Get axis-grouped dimensional breakdown for an entity

Returns the dimensional decomposition of a metric grouped by XBRL axis. Includes reconciliation (sum_to_consolidated) and is_additive flag. Without the facts.premium scope, the axes are listed with their consolidated totals but members is empty.

metric is OPTIONAL. Omit it to let the service elect one it can actually render (metric_selection=auto_selected). Supply it and it is never replaced by another: an entity that does not tag that metric dimensionally yields the same metric with axes: [] and metric_selection=requested_not_dimensional, and available_metrics lists what it does tag. Read metric_selection, not just metric.