android: fix key regeneration, Clear DB, uasync eventfd, udp log from config

- jni_on_event: fix JNI_EDETACHED — AttachCurrentThread/DetachCurrentThread
- u_async.c: pipe→eventfd for reliable cross-thread wakeup
  add process_posted_tasks in poll() path, fix EINTR (saved_errno)
- bridge_debug_hook: keep udp_log_write, remove mutex from udp_log
- memory_pool.c: alloc/free logs INFO→DEBUG (reduce spam)
- instance_lite.c: chat_event_set_handler before ensure_keys,
  KEYS_GENERATED events, fchmod 0600 on keys.conf,
  UDP log from config [log_udp] section, regenerate_trampoline
- config_parser: parse [log_udp] ip/port
- NativeLib.kt: remove callbacksSet, simplify init/stop/destroy
- ChatViewModel.kt: unified event callback in init, pubKey StateFlow,
  requestRegenerateKeys, clearState fix
- SettingsScreen.kt: pubKey.collectAsState(), Clear DB via restart()
- HeadlessService.kt: remove setUdpLogTarget (now from config)
- android_udp_log.c: simplified — no mutex, buffer+send+timer in one thread
- utun_instance.c: NULL-check tcp_connections before destroy
- chat_event.h: +CHAT_EVT_KEYS_GENERATED 11, -NODE_CHANGED
- logreceiver: UDP log receiver tool

tools/chatgui-android/app/src/main/cpp/CMakeLists.txt

@@ -35,6 +35,7 @@ set_target_properties(utun_core PROPERTIES C_STANDARD 99 C_STANDARD_REQUIRED ON)
 # JNI bridge + link into shared library
 add_library(utun SHARED
     ${JNI_DIR}/android_jni_bridge.c
+    ${JNI_DIR}/android_udp_log.c
     $<TARGET_OBJECTS:utun_core>
 )