Allow Discord guild registration to accept multiple values; Allow custom rate limiting for each #112
Description
We should let the bot register commands in more than one guild and support per‑guild rate‑limit overrides.
Today we require a single DISCORD_GUILD_ID, which makes multi‑server deployments awkward and forces global limits.
Proposal: accept a comma‑delimited list (or auto‑discover guilds), register commands per guild, and add a simple per‑guild override mechanism for rate limiting - possibly through a small config file.