android: real utun instance + SQLite channels + reactive logs + QR join

- instance_lite.h/c: full uTun stack from INI config text
  (keygen, uasync, UTUN_INSTANCE, SQLite, chat_core/sync, BGP, etcp_router)
- jni_bridge: nativeStart/Stop, nativeJoinChannel → chat_sync_connect_from_invite,
  nativeSubscribeLogs, C logs → logcat + Kotlin LogManager
- Kotlin: direct read-only SQLite queries (channels, messages),
  ViewModel with live event callbacks, reactive LogScreen (tail -f),
  CameraX QR scanner with proper lifecycle, JoinChannelDialog
- HeadlessService: generates INI config from Kotlin settings → C instance

lib/debug_config.h

@@ -157,6 +157,10 @@ void debug_output(debug_level_t level, debug_category_t category_idx,
                  const char* function, const char* file, int line,
                  const char* format, ...);
 
+/* Log hook — if set, called with every debug message (for JNI/bridge integration) */
+typedef void (*debug_log_hook_fn)(int level, const char* category, const char* message);
+void debug_set_log_hook(debug_log_hook_fn hook);
+
 /* Parse debug configuration from string (e.g. "etcp=trace,config=info") */
 int debug_parse_config(const char* config_string);