Users sometimes paste Discord IDs with prefixes like 'user:123456',
'<@123456>', or '<@!123456>' from Discord's UI or third-party tools.
This caused auth failures since the allowlist contained 'user:123' but
the actual user_id from messages was just '123'.
Fixes:
- Added _clean_discord_id() helper in discord.py to strip common prefixes
- Applied sanitization at runtime when parsing DISCORD_ALLOWED_USERS env var
- Applied sanitization in hermes setup and hermes gateway setup input flows
- Handles user:, <@>, and <@!> prefix formats
153ccbfd61