feat(hub): one account, several linked nodes

An account links up to MAX_NODES_PER_ACCOUNT node keys (node_keys table)
instead of the one users.pk_node_ed25519; the migration carries each
account's key over and the downgrade keeps the last one linked.
/v1/nodes/auth accepts any linked key, and its token names the key that
won it (nk). PUT /me/node_key adds a key, idempotently, 409 past the
limit; DELETE /me/node_key names the key: a browser session any of its
own, a node only its own. Unlinking a key closes that node's socket and
refuses its tokens at once, on REST and on the socket; the account's other
nodes are untouched. /pubkeys no longer gives a node key to other accounts,
and gives the caller its last linked one, which installed desktop apps read.

The node reports waiting_for_node_key while its key is unlinked and signs
in again as soon as the hub says so, so a key linked again is back within
seconds; unlinking itself signs in first to hold a token naming its key.

Profile -> Linked nodes lists each node (connected, last seen, IP, linked
since, This machine in the desktop app) with Copy and Unlink, and adds a
key by hand. The Node page banner, Create group and the desktop app add
this machine's key instead of replacing another's. Messages that pointed
at Settings -> Link Node point at Profile -> Linked nodes.

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

1 files changed, 4 insertions, 3 deletions

diff --git a/docs/USERGUIDE.md b/docs/USERGUIDE.md
index e8bd8fb..5b6f77a 100644
--- a/docs/USERGUIDE.md
+++ b/docs/USERGUIDE.md
@@ -1069,9 +1069,10 @@ anything missing.
 **"No nodes are currently online for this group."**
 The node is not running, is not reachable, or has not linked its key to the
 hub. On the node: `meshbay-node status`, then Step 4 and 5 of the quickstart.
-In the desktop app, the **Node** page says when your account is linked to the
-node of another machine (**Link this node instead**); **Profile → Unlink**
-lets go of a node from anywhere, for a machine that is gone.
+In the desktop app, the **Node** page says when this machine's node is not
+linked to your account (**Link this node**). **Profile → Linked nodes** lists
+every node your account has linked, one per machine, and **Unlink** lets go of
+one from anywhere — for a machine that is gone — without touching the others.
 
 **A member sees the group but no files.**
 They never redeemed an invitation code, or the group has no key