Wow, the current incarnation RATP website is indeed missing a lot of information. (The French version used to be a lot better, and the English version used to completely omit commuter passes. Looks like they've now aligned the version, but they've removed a lot of information.)
RATP is just one of the agencies that run public transport in the Paris area, so you can also look for information in other places such Navigo (agency that manages the Navigo pass, French only) or SNCF Transilien (the agency that runs the suburban trains, French and English). Both correctly state that a Navigo weekly pass is valid from Monday to Sunday (and likewise a Navigo monthly pass is valid from the first to the last day of a calendar month).
The most official source is the terms of service (French only, not searchable or accessible to screen readers). The official rules state that the pass is valid from Monday 0:00 to Sunday 23:59. The cutoff time is the time when you enter the metro or heavy rail network, or the time when you board a bus or tram, you can finish the last leg of your journey after midnight. There's an exception for the night buses (Noctilien): on Noctilien services, the pass is valid both on the Monday morning at the end of the validity period and as the Monday morning at the beginning of the validity period.
The addendum about zones on the week-end (“dézonage”) does not apply to weekly passes, only to monthly passes. If you have a 2-zone weekly pass, it's only valid in these two zones, period. If you have an all-zone weekly pass, it's valid throughout the Île-de-France region.