Move neutral join/leave handlers into GmRelay.Shared so Telegram and Discord share capacity, waitlist, duplicate-click, and schedule-update behavior.
Add Discord component routing for join_session and leave_session buttons with deferred ephemeral replies and serialized schedule message updates.
Bump version to 2.5.0 and update Discord docs.
Refs #29
Convert join/leave interaction commands to PlatformUser, PlatformGroup, and PlatformMessageRef. Persist and look up participants by platform identity while keeping Telegram callbacks intact. Add V017 migration and TDD coverage. Bump version to 2.1.1.