[fix](trx-server): start audio capture when decoder tasks are subscribed

The capture thread only checked Opus broadcast subscribers to decide
whether to start cpal input. PCM tap subscribers (APRS/CW decoders)
were not considered, so decoding never started without a browser
audio client. Include pcm_tx receiver count in the has_receivers
check.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Stanislaw Grams <stanislawgrams@gmail.com>

src/trx-server/src/audio.rs

@@ -110,7 +110,8 @@ fn run_capture(
     let mut capturing = false;
 
     loop {
-        let has_receivers = tx.receiver_count() > 0;
+        let has_receivers = tx.receiver_count() > 0
+            || pcm_tx.as_ref().map_or(false, |p| p.receiver_count() > 0);
 
         if has_receivers && !capturing {
             let _ = stream.play();