feat(hub): make mailing an invitation a remembered choice

A "Send the invitation by e-mail" box under the Invite member field,
checked by default and stored as the invite_email preference. Unchecked,
invite-notify is never called and the hub never sees the code.

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

1 files changed, 11 insertions, 3 deletions

diff --git a/docs/USERGUIDE.md b/docs/USERGUIDE.md
index 0dd5819..d7c3430 100644
--- a/docs/USERGUIDE.md
+++ b/docs/USERGUIDE.md
@@ -220,9 +220,10 @@ Someone who runs a node invites you. You need an account on the same hub first.
 
 You will not be asked again on that browser, or on that machine.
 
-**The code never passes through the hub**, and that is the whole reason it
-exists: it proves the invitation came from the person running the group, and
-not from the service in the middle.
+**The code never passes through the hub** — unless whoever invited you asked
+the hub to mail it to you — and that is the whole reason it exists: it proves
+the invitation came from the person running the group, and not from the
+service in the middle.
 
 ### Leaving
 
@@ -548,6 +549,13 @@ membership on the hub and produces a code that never goes near it. Send the
 code out of band; they enter it the first time they open the group. You do not
 need to be online then.
 
+The Members tab offers **Send the invitation by e-mail**, ticked by default: the
+hub mails the code to the address on their account, so nobody has to copy it.
+That is a trade: **the hub then holds the code**, and a hub that wanted to could
+use it to join in their place. For a group where that matters, untick it and
+send the code yourself — the box remembers your choice. The CLI never mails
+anything.
+
 ### Seeing who is in
 
 ```bash