Introduce PlugNMeetWebhookAPIView to handle:
- room_finished: close live session and mark users offline
- participant_joined: create/reactivate LiveSessionUser
- participant_left: mark user offline with exit timestamp
- end_recording: fetch info, obtain token, download file, save
LiveSessionRecording, and generate video thumbnails via ffmpeg
Add new PlugNMeetClient methods:
- get_recording_info
- get_recording_download_token
- download_file
Expose webhook route at /api/course/plugnmeet/webhook/ with HMAC
SHA256 signature verification (Hash-Token header).
Deprecate polling-based room status sync in
CourseOnlineClassTokenValidateAPIView in favor of webhooks.
build(docker): add ffmpeg to production image for thumbnail generation
docs: add webhook setup and usage guides (README_WEBHOOK.md,
docs/plugnmeet_webhook.md)
chore(scripts): add create_live_room.sh and scripts/test_webhook.py for
manual testing and workflow support
