UserContextMenuRegistry

Maps each user context-menu command name to a presence marker. Populated by seedcord codegen, which reads every command's toJSON() and emits a declare module '@seedcord/gateway' augmentation, so keyof UserContextMenuRegistry is the compile-time union of every registered user context-menu name. Do not augment it by hand, run seedcord codegen.

Kept separate from MessageContextMenuRegistry because Discord allows a user command and a message command to share a name, so a single name-keyed registry would collapse a legal pair.