fix(cw): activate the Kenwood/Elecraft keyer engine when selected

The frontend engine loader had no "kenwood" case, so a saved engine of
"kenwood" fell through to the WinKeyer default — the Kenwood/Elecraft
CW-over-CAT engine never ran even though the setting showed it selected.

Also clarify the Kenwood data-mode comment: there is no single mode digit
right for both a K3 (DATA=MD6) and a TS-590SG (MD6=FSK), so data stays on
USB as the safe common base; a rig-specific DATA mode is a follow-up.

frontend/src/App.tsx

@@ -2706,8 +2706,9 @@ export default function App() {
         s.engine === 'icom' ? 'icom'
           : s.engine === 'flex' ? 'flex'
             : s.engine === 'yaesu' ? 'yaesu'
-              : s.engine === 'serial' ? 'serial'
-                : 'winkeyer');
+              : s.engine === 'kenwood' ? 'kenwood'
+                : s.engine === 'serial' ? 'serial'
+                  : 'winkeyer');
     } catch { /* keyer not configured */ }
   }, []);