fix(client): say when the account's node is elsewhere, and let go of it

Signing in on a desktop links this machine's node to the account, but never
over a key already linked (that would cut off the user's other machine) nor a
node set up for another account. On a real install both left the node reading
"Running" while the hub refused it in a loop, and nothing said why. And the
only way to unlink was the linked machine's own Node page, of no use once
that machine is gone.

- The Node page works out, from the node and the hub each time it looks,
  whether this node can serve the signed-in account (nodeLinkProblem), and
  says why not: "Link this node instead" (asked first) puts this node's key
  on the account; "Use this node for my account" switches a node set up for
  another account through node:start, which takeOver now lets past a node
  that answers "running". The first version went through node:start for
  both, and clicking it on a real install did nothing: a node signed in
  before the account was linked elsewhere answers "running".
- The Profile page unlinks the account's node (DELETE /v1/users/me/node_key),
  from any machine.

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

1 files changed, 6 insertions, 3 deletions

diff --git a/docs/PACKAGING-GUIDE.md b/docs/PACKAGING-GUIDE.md
index a9aa7fc..9f5d6cf 100644
--- a/docs/PACKAGING-GUIDE.md
+++ b/docs/PACKAGING-GUIDE.md
@@ -102,10 +102,13 @@ Two cases where the app does not do it on its own, because it would undo
 something:
 
 - the node was already set up for **another account or another hub** — the
-  **Start** button on the Node page asks before switching it;
+  Node page says so, and **Use this node for my account** asks before
+  switching it;
 - your account is already linked to a node on **another machine** — linking
-  this one would disconnect that one. The Node page shows this node's key;
-  **Profile → Link Node** moves the link here if that is what you want.
+  this one would disconnect that one. The Node page says so, and **Link this
+  node instead** asks before moving the link here. **Profile → Unlink** lets
+  go of the other machine's node from anywhere, which is the way out when that
+  machine is gone.
 
 The Node page's **Start / Stop / Restart** work in every mode, and its status
 is the node's own: **Running** when it answers, **Stopped** only once no