register_guild_commands
Standalone script that registers all slash commands with a specific Discord guild.
Usage: npx esrun register_guild_commands.ts
Reads every command module from commands/<category>/*.js, serialises
them to JSON, and PUTs the full set to the Discord REST API using
Routes.applicationGuildCommands. This is guild-scoped registration
(instant updates) rather than global registration (up to 1-hour propagation).
Required environment variables: DISCORD_TOKEN, BOT_SELF, GUILD_ID.