fix: only the owner decides who hosts a group, and nobody is made a member unasked

- hub: a node may host a group only if its account owns it or the owner
  approved that node (new `group_hosts`). Membership was the ceiling, and
  every member holds the group key, so any member's node could register as a
  host and be the one clients kept. A node claiming a group it may not host
  is recorded as a request; the owner is notified once and approves or
  refuses it (GET/POST/DELETE /v1/groups/{id}/hosts[/{node_id}]), which
  takes effect on a connected node at once.
- hub: an owner adding a username creates an invitation (new
  `group_invitations`), accepted or declined by the invitee
  (/v1/groups/invitations, /{id}/invitation/accept|decline). Until then the
  group is not listed, not dialled, not searched and not in any token.
  Invitation links, open joins and group creation still make members
  directly: they are the account's own act.
- hub: the MNP token names only the group it is minted for (group_id is now
  required), so a node operator no longer learns a member's other groups.
- SPA: invitations on the home page; invited people and host requests in
  the group's settings; the transport sends group_id. Ten catalogues.
- Browser probes for both screens, run in Chrome and Firefox.
- Design §5.2, §7.2, §7.3, AV32, AV33; protocol §6.3; user guide.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/docs/MESHBAY_NODE_PROTOCOL.md b/docs/MESHBAY_NODE_PROTOCOL.md
index 2e5aca3..70047b2 100644
--- a/docs/MESHBAY_NODE_PROTOCOL.md
+++ b/docs/MESHBAY_NODE_PROTOCOL.md
@@ -489,8 +489,10 @@ would let whoever issues tokens decide it instead. Identity keys are pinned by t
 node's roster. The hub certifies accounts, not keys.
 
 `not_a_member` means the hub did not count this account a member of the group when it
-minted the token. The MNP token is minted for each connection, from the membership the
-hub holds at that moment, so a stale `groups` claim is no longer the usual cause; the
+minted the token. The MNP token is minted for each connection and names **only** that
+connection's group (`POST /v1/nodes/mnp-token {node_pk, group_id}`; `groups` is empty
+for a non-member), so the operator it is handed to learns nothing of the member's
+other groups. A stale `groups` claim is therefore no longer the usual cause; the
 client still refreshes its session once and retries on that code before telling someone
 who was just invited that they are not a member.