fix: Android event handler lost after restart — g_event_handler now preserved

Root cause: instance_lite_restart was creating new thread without
re-setting g_event_handler, causing all chat events (CHANNEL_UPDATED,
CONNECT_RESULT, etc.) to be silently dropped after app restart.

Fixes:
- instance_lite_restart: save/restore g_event_handler across hard restart
- instance_thread restart loop: re-call chat_event_set_handler after uasync_create
- utun_bridge_restart: call instance_lite_set_event_handler before restart
- AppEventHandler SharedFlow replay: 1 → 16 to not lose early init events
- ViewModel: added diagnostic logging for channel/connect events
- Keep diagnostic logs in instance_lite (set_handler, chat_event_forward NULL check)
- instance_event_handler: removed static for cross-block forward declaration

tools/chatgui-android/app/src/main/java/com/utun/chat/ChatApplication.kt

@@ -10,7 +10,7 @@ import kotlinx.coroutines.flow.MutableSharedFlow
 import kotlinx.coroutines.flow.SharedFlow
 
 object AppEventHandler : ChatEventCallback {
-    private val _events = MutableSharedFlow<Pair<Int, ByteArray?>>(replay = 1, extraBufferCapacity = 64)
+    private val _events = MutableSharedFlow<Pair<Int, ByteArray?>>(replay = 16, extraBufferCapacity = 64)
     val events: SharedFlow<Pair<Int, ByteArray?>> = _events
 
     override fun onEvent(type: Int, data: ByteArray?) {

tools/chatgui-android/app/src/main/java/com/utun/chat/viewmodel/ChatViewModel.kt

@@ -181,7 +181,7 @@ class ChatViewModel : ViewModel() {
                 }
             }
             2 -> { /* CONNECT_RESULT: [node_id:8][result:4][channel_id:8] */
-                if (repo == null || data == null || data.size < 20) return
+                if (repo == null || data == null || data.size < 20) { LogManager.addLog("WARN", "VM", "CONNECT_RESULT skipped repo=${repo != null} data=${data != null}"); return }
                 val buf = java.nio.ByteBuffer.wrap(data).order(java.nio.ByteOrder.LITTLE_ENDIAN)
                 val nodeId = buf.getLong()
                 val result = buf.getInt()
@@ -189,9 +189,10 @@ class ChatViewModel : ViewModel() {
                 LogManager.addLog(
                     if (result == 0) "INFO" else "ERROR",
                     "JOIN", "connect to 0x%016x ch=$chId result=$result".format(nodeId))
+                LogManager.addLog("INFO", "VM", "CONNECT_RESULT result=$result — refreshChannels")
                 if (result == 0) refreshChannels()
             }
-            4 -> if (repo != null) refreshChannels()  /* CHANNEL_UPDATED */
+            4 -> { if (repo != null) { LogManager.addLog("INFO", "VM", "CHANNEL_UPDATED — refreshChannels"); refreshChannels() } else { LogManager.addLog("WARN", "VM", "CHANNEL_UPDATED skipped — repo is NULL") } }
             12 -> LogManager.addLog("INFO", "VM", "service started")
             13 -> LogManager.addLog("INFO", "VM", "service stopped")
             16 -> { /* NODEINFO_UPDATED: [node_id:8][presence:1][up:1][best_rtt:2] */