Adds a new cohort view that helps users track how groups of records evolve over time, making it easier to analyze retention and revenue trends. The subscription dashboard now uses this standard view, with Studio editing support and Excel export for easier reporting.

* Task: https://www.odoo.com/web#id=29402&view_type=form&model=project.task&action=327&menu_id=4720
* Pad: https://pad.odoo.com/p/r.241110e82b471a377043ef793f229a50