Implements discord.py Bot Gateway to receive @agent mentions and enqueue tasks.
Includes deterministic thread ID generation and message parsing for issue numbers,
repo names, and freeform requests. Supports message queuing for running threads.
Files:
- agent/integrations/discord_handler.py: DiscordHandler class with event handling
- tests/test_discord_handler.py: 4 tests for parsing and thread ID generation
All tests pass (95 total).
