refactor: the account pane becomes Fields, the pane for anything but a secret

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/app/help.go

@@ -36,7 +36,7 @@ type contextHelp struct {
 	k        keys.Map
 	focus    pane
 	commands bool // custom commands apply here
-	account  bool // the fourth pane describes an account (source_detail.go)
+	account  bool // the fourth pane describes an account (fields.go)
 }
 
 func (c contextHelp) ShortHelp() []key.Binding {