fix: no play-on-air button on CW

In CW the transmitter builds its tone from the keyer and ignores the DAX TX
audio path, so the button keyed the rig and sent silence. Confirmed on a Flex:
our side reported the playback as done while nothing went out.

Only the button goes. The row stays, or a CW operator who stopped their
recording would be left with no way to resume it — and the recording itself is
still worth keeping.

frontend/src/App.tsx

@@ -3739,17 +3739,24 @@ export default function App() {
       {/* A stopped take: play it to the station being worked, or carry on
           recording. Both sit where the counter is, which has shifted left to
           make room. */}
+      {/* A stopped take: resume it, and — on PHONE only — play it to the station
+          being worked. In CW the transmitter builds its tone from the keyer and
+          ignores the DAX TX audio path entirely, so the button would key the rig
+          and send silence. The row itself stays, or a CW operator who stopped
+          would be left with no way to resume. */}
       {recording && recStopped && RECORDABLE_MODES.has(mode.toUpperCase()) && (
         <span className="absolute right-2 top-1/2 -translate-y-1/2 z-10 inline-flex items-center gap-1.5">
-          <button
-            type="button"
-            onMouseDown={(e) => e.preventDefault()}
-            onClick={playRecordingOnAir}
-            title={t('rec.playOnAir')}
-            className="inline-flex items-center justify-center size-4 rounded text-success hover:bg-success/15"
-          >
-            ▶
-          </button>
+          {PHONE_MODES.has(mode.toUpperCase()) && (
+            <button
+              type="button"
+              onMouseDown={(e) => e.preventDefault()}
+              onClick={playRecordingOnAir}
+              title={t('rec.playOnAir')}
+              className="inline-flex items-center justify-center size-4 rounded text-success hover:bg-success/15"
+            >
+              ▶
+            </button>
+          )}
           <button
             type="button"
             onMouseDown={(e) => e.preventDefault()}