Faga's Discord Bridge

This release improves security, reliability, and setup UX for Discord bridge configuration.

• Added /config slash command for Discord admins to set:
  • chat_channel_id
  • admin_channel_id
  • whitelist_guild_id
• Replaced legacy text setup flow (!bridge setup, !bridge chat, !bridge admin) with /config.
• Security fix: switched config type from SERVER to COMMON to prevent server config sync leaking sensitive values (like Discord bot token) to clients.
• Config file path changed to config/mcdiscordbridge-common.toml.
• Removed message-content-intent-dependent setup logic and removed enableMessageContentIntent.
• Added safeguards for inaccessible Discord channels and hardened send/fallback error handling to prevent server crashes.
• Fixed Makefile NeoForge version auto-resolution used by make run-prod-local / make run-local-one.