fix(android): pass PROTOCOL_DNS_SD so mDNS registration works

Android 16 added NsdManager.checkProtocol(): registerService with protocol
0 threw IllegalArgumentException: Unsupported protocol — silently, since
the old code swallowed the exception into a dead reflection fallback and
start() overwrote the failure status with the Listening line. mDNS never
actually advertised (the Phase 8 session streamed via --peer, masking it).

Also advertise after the listening status so a registration failure stays
visible, and log the exception and the registration success.

Validated live on the Fairphone 6: the desktop --discover lists the phone
and a full --send session decodes (in-band SPS 320x240 -> 2496x1040) and
renders.

android/app/src/main/kotlin/screen_cast/pipeline/ReceiverPipeline.kt

@@ -110,11 +110,13 @@ class ReceiverPipeline(
 
         running = true
         readerThread = Thread({ readLoop() }, "rtp-reader").also { it.start() }
-        advertiseNsd(signalingPort)
+        // Advertise AFTER the listening status: a registration failure must
+        // not be overwritten by it (both post to the same overlay).
         onStatus(
             "Listening on $localIp (media :$udpPort, signaling :$signalingPort)\n" +
                 "Waiting for a sender… (fall back to: screencast --send --peer $localIp:$signalingPort)",
         )
+        advertiseNsd(signalingPort)
     }
 
     /**
@@ -345,6 +347,7 @@ class ReceiverPipeline(
         val listener = object : NsdManager.RegistrationListener {
             override fun onServiceRegistered(serviceInfo: NsdServiceInfo) {
                 // Registered: the sender's mDNS browser should see it now.
+                android.util.Log.i(TAG, "mDNS registered: ${serviceInfo.serviceName}.${SERVICE_TYPE}")
             }
 
             override fun onServiceUnregistered(serviceInfo: NsdServiceInfo) = Unit
@@ -356,9 +359,14 @@ class ReceiverPipeline(
             override fun onUnregistrationFailed(serviceInfo: NsdServiceInfo, errorCode: Int) = Unit
         }
         try {
-            nsdManager.registerService(info, 0, listener)
+            // PROTOCOL_DNS_SD is mandatory on API 36: NsdManager.checkProtocol()
+            // rejects anything else (the historical 0 threw
+            // "IllegalArgumentException: Unsupported protocol", which the
+            // old code swallowed — mDNS never advertised on this phone).
+            nsdManager.registerService(info, NsdManager.PROTOCOL_DNS_SD, listener)
             registrationListener = listener
         } catch (e: Exception) {
+            android.util.Log.e(TAG, "mDNS registration failed", e)
             onStatus("mDNS unavailable (${e.message}) — reach this receiver with --peer $localIp:$port")
         }
     }