Users can now join webinar even if it's already started:
- isWebinarJoinable(): returns true if current time <= event_start + duration
- isWebinarEnded(): returns true if current time > event_start + duration
- "Gabung Webinar" button shows as long as webinar hasn't ended
- This allows latecomers to join immediately
Previously used only event_start which prevented joining after start time.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>