v0.26.0

What's Changed

• refactor(core): extract MembershipMixin from RoomLifecycleMixin
• docs(changelog): document membership/read-markers, stamp 0.26.0 (2026-07-10)
• style(tests): format test_participant_membership.py
• feat(rooms): explicit membership (join/leave) + read-marker aggregation
• feat(threading): flat two-level message threads on parent_event_id
• Begin 0.26.0.dev0 development

Full Changelog: v0.25.0...v0.26.0