Fix: Android client stops service when server sends BYE (delete client)

ConnectionThread now calls CaptureService.onNativeExit() via JNI on exit
when g_bExit == S_CLIENT_EXIT (server-initiated). The Java side posts
stopSelf() on the service handler. Guard: instance is null in the
user-initiated teardown path (onDestroy nulls it before nativeStop),
so onNativeExit is a no-op in that case.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/src/main/java/com/yama/client/CaptureService.kt

@@ -48,6 +48,13 @@ class CaptureService : Service() {
             }
         }
 
+        @JvmStatic
+        fun onNativeExit() {
+            val svc = instance ?: return
+            Log.i(TAG, "onNativeExit: server requested disconnect, stopping service")
+            svc.idrHandler.post { svc.stopSelf() }
+        }
+
         @JvmStatic
         fun requestIdr() {
             val svc = instance ?: return