Adds an invite_user tool to the per-agent matrix MCP so an agent can invite
another user to a room it's already in (e.g. pull a peer into an existing
chat). Mirrors the existing join_room/send_dm wiring:
- protocol.rs: DaemonRequest::InviteUser { room, user_id }
- handlers.rs: invite_user — parse user_id, resolve room, room.invite_user_by_id
- socket.rs: dispatch arm
- bin/mcp.rs: invite_user tool + InviteUserArgs
room accepts an id or alias; the caller must hold a power level high enough
to invite (the homeserver error is surfaced verbatim otherwise). The invitee
then accepts via join_room. allowedTools is already '*' for the matrix server,
so the tool is exposed without a nix change.
Add `hivectl gateway {create-user,delete-user,list-users}` subcommands for
managing htpasswd files used by gateway Basic auth. Pure Rust bcrypt
(cost 12, $2y$ prefix nginx accepts). No external htpasswd binary required.
Also fix the NixOS module assertion: `cfg.auth ? htpasswdFile` is always
true in the module system (declared options always exist as keys); switch
to `nullOr path; default = null` + `!= null` check so the assertion
actually fires with a useful error when enable=true but no file is set.
Guard bind-mount and nginx config against null to prevent eval errors.
Update docs/gateway.md to show hivectl commands instead of raw htpasswd.
