OR logic in segments

Segments can now match customers who fit any one of several rule groups, not just a single list of conditions.

Build groups of criteria where everything inside a group must match, then add alternatives with Add OR group. For example: (active members on an unlimited plan) OR (anyone who reserved five or more classes). Existing segments keep working exactly as before, and single-group segments look the same as they always have, now with an explicit AND connector between conditions.