Drive the connection manager from the keyboard

The manager had only Esc and the scale keys: its list took one Tab stop
per row with no arrows, a stack's rename / delete / open-in-tabs buttons
existed only on hover, and no action had a key.

- Commands (the manager keymap scope, remappable like the rest): new
  connection with focus in Name, new stack, save, connect — or open the
  focused stack in tabs — delete the focused row, rename the focused
  stack, import from WinSCP, close the window.
- The list: up/down/Home/End move focus between rows (focus only:
  loading a connection would discard a half-edited form), Enter opens the
  focused connection, left/right collapse and expand a stack, and a
  stack's actions show while the keyboard is in its row.
- Enter in a form field connects; Esc leaves a field before it closes the
  window; Tab is walked by hand (WKWebView skips buttons and radios); focus
  comes back after a dialog and never stays lost on <body>.
- Tooltips show the keys; the Settings → Keyboard fixed-key list gains the
  manager's.

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

docs/gotchas.md

@@ -299,6 +299,10 @@ touching the adjacent code.
   j/k) must resolve BEFORE it — and then that letter no longer starts a query
   (Settings warns). While a query is being typed, printable keys (Space too)
   always extend it.
+- **In a master-detail list, selection must not follow focus** when the detail
+  is an unsaved form: the connection manager's `edit()` replaces the draft
+  without asking, so arrowing through the list would silently discard edits.
+  Arrows move focus; Enter loads.
 - **A dialog's Esc must `stopPropagation`.** The connection manager closes on
   a window-level Escape; the dialog cleared its own signal first, so the
   window handler saw "no dialog open" and closed the whole window.