dashboard: keys edited, the last removed with a password, failures kept

The credentials dialog listed a user's keys whole, to add one or
remove one but the last, and any failure replaced the dialog with the
error, the form lost.

* A key is shown short: its type, the first and last four characters
  of what tells it apart (an Ed25519 key's base64 after the part all of
  them share), its comment; the whole line in its tooltip.
* A key can be edited, its name and its line: saved under the name, a
  new name written first and the old one removed.
* A user with a password on this node (`--htpasswd`) may remove its
  last key: it logs in by the password. GET /auth/keys says so
  (`password`), and DELETE /auth/keys/{id} takes it then; the rules no
  longer keep the last key on every node (no other node can tell who
  has a password where; under a strict policy the signed entry keeps
  one still).
* What fails says why beside where it was asked (the add form, the
  edited row, the removed one), which stays as it was, to be set right
  and tried again.

1 files changed, 4 insertions, 2 deletions

diff --git a/docs/access.md b/docs/access.md
index 2df7270..4bb5945 100644
--- a/docs/access.md
+++ b/docs/access.md
@@ -36,8 +36,10 @@ password hashes: every member reads the document).
   with the line, `DELETE /auth/keys/<name>`; under a strict policy, by signing its
   entry with only its keys changed (`continuum-signed key-add laptop
   ~/.ssh/id_ed25519.pub`, `key-remove laptop`), with a key it holds already. Every
-  node takes that from the user itself, as from one who may manage users, but never
-  its last key removed (`409`): one who may manage users may.
+  node takes that from the user itself, as from one who may manage users. Its last key
+  it removes only on a node where it has a password (`--htpasswd`), which it logs in
+  by then (`409` elsewhere); under a strict policy, never (it signs its entry with
+  one).
 
 ## A new swarm