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.

docs/PHASES.md

@@ -114,6 +114,13 @@ existing signaling + RTP protocol; no C++ changes.
       depacketizer — 25 tests green)
 - [x] 8.3 Signaling + NSD validated on device (offer → answer over the
       network; mDNS registration via the API-36 RegistrationListener)
+      — **correction 2026-09-10**: registration had in fact never
+      succeeded (registerService passed protocol `0`, which API 36
+      rejects with "Unsupported protocol"; the swallowed failure was
+      hidden behind the "Listening…" status). Fixed with
+      `PROTOCOL_DNS_SD` + real on-device validation: desktop
+      `--discover` lists the phone and a live `--send` session
+      decodes and renders.
 - [x] 8.4 MediaCodec decode + Surface render validated on device (in-band
       SPS sizing, letterbox fit)
 - [x] 8.5 End-to-end on a Fairphone 6 (Android 16): streaming, letterboxed

docs/RUNBOOK.md

@@ -240,6 +240,16 @@ Platform quirks found while validating (Android 16 / API 36):
 
 - `android.permission.INTERNET` is required — NsdService rejects
   registration without it.
+- `NsdManager.registerService` on Android 16 validates the protocol
+  argument (`NsdManager.checkProtocol`): the historical `0` throws
+  `IllegalArgumentException: Unsupported protocol` — pass
+  `NsdManager.PROTOCOL_DNS_SD`. This was silent for a long time: the app
+  swallowed the exception and the failure status was overwritten by the
+  "Listening…" line, so mDNS never advertised even though the UI looked
+  fine (discovery only worked via `--peer`). Diagnosed via
+  `adb shell dumpsys servicediscovery` (the client's `mClientRequests`
+  stays empty when no request was ever issued) plus logging the
+  exception.
 - `DatagramSocket.localPort` gives the bound port; `.port` is -1 for
   unconnected datagram sockets, and `.localAddress` is an `InetAddress`
   (Inet6Address on Android), not an `InetSocketAddress`.