Rework the telnet window's cluster favourites and login tabs

Favourites show the callsign in bold, the address and the sysop's note,
and each keeps its own password, commands, logon call and note. Clicking
one fills the boxes for editing. Autoconnect marks the favourite to
connect to at start and replaces the old reconnect-to-last-node setting.
A new published list refreshes the notes of the favourites in it. The
published list now spans the window, and the Spot comment tab becomes
Login & Spots with the logon call and keep-alive.

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

README.md

@@ -953,12 +953,18 @@ tabs, the ones N1MM has:
   spot line, or "Jump to this spot" on the right-click menu, puts the radio
   there with the call in the entry window. Scrolling stops while the pointer is
   over the traffic, so a line can be read while the node keeps sending.
-- **Clusters** keeps a list of nodes with their names, ports, passwords and the
-  commands to send after login. Connect and Disconnect are there, with automatic
-  logon, the call to log on with, and the keep-alive interval. **Download** under
-  it fetches the published list of nodes from
+- **Clusters** keeps a list of favourite nodes: the callsign in bold, the
+  address and, under them, the sysop's note. Each favourite has its own password,
+  its own commands to send after login and its own call to log on with (empty
+  means the one on the Login & Spots tab). Clicking a favourite fills the boxes
+  so it can be edited, and **Save** writes the change back. **Autoconnect** marks
+  one favourite as the node to connect to when the program starts and moves it to
+  the top; on that favourite the button reads **Don't connect**, and with no
+  favourite marked nothing connects at start. **Download**, across the bottom,
+  fetches the published list of nodes from
   [NG3K](https://www.ng3k.com/misc/cluster.html) — around fifty nodes with the
-  sysop's call, the address and a note about each — and clicking one fills the
+  sysop's call, the address and a note about each — and refreshes the notes of the
+  favourites that are in it. Clicking a node in the list fills the
   boxes in. N1MM downloads its list from its own web service, which asks the
   operator to opt in to data collection; this reads a public page instead.
 - **Filters** says which spots reach the bandmap: bands, modes, beacons, busted
@@ -970,7 +976,8 @@ tabs, the ones N1MM has:
   sends.
 - **Buttons** edits the twelve command buttons: a label and its commands, or
   back to the defaults.
-- **Spot comment** is what goes out with the spots you send.
+- **Login & Spots** holds the call to log on with, the keep-alive interval and the
+  comment that goes out with the spots you send.
 
 The buttons come from the settings; without any, they are `sh/dx`, `sh/dx/20`,
 `sh/wwv`, `sh/users`, `sh/c/n`, `help` and `bye`. A button holds what N1MM's
@@ -1020,7 +1027,7 @@ retried. The last two hundred lines are kept, so a window opened mid-contest is
 not blank.
 
 Alt+P, or **Edit → Spot It**, puts the call being typed on the cluster at the
-current frequency, with the comment from the Spot comment tab — which takes the
+current frequency, with the comment from the Login & Spots tab — which takes the
 message macros too; with nothing
 typed it spots the last contact logged. The spot also goes straight onto our own
 bandmap rather than waiting to come back round from the node.