build: extract libutun.a from src/ + add db_sync module + etcp API, BBR improvements

- Add libutun.a (noinst) containing all src/*.c except utun.c
- utun binary now links libutun.a + libuasync.a
- tests/Makefile.am simplified: all tests link libutun.a instead of
  manual .o file lists (removed ~70 lines of boilerplate)
- Add db_sync module: distributed content-addressed DB with LMDB
  backend, peer-to-peer sync via etcp_router (svc 0x20)
- etcp API: etcp_send_in_order(), etcp_clear_inflight_queues(),
  verify_packet_signature(), BBR getters
- BBR: adaptive threshold (1/4 of pipe-min instead of hardcoded)
- route_bgp/etcp_connect: STCP transport support in NODEINFO
- conn_mgr: NODEINFO_ADDRS doc for nat_type/transport/proto fields
- Cleanup: removed AUDIT_FINDINGS.txt, filelist.txt, nat.txt

src/utun_instance.c

@@ -12,6 +12,7 @@
 #include "etcp_connections.h"
 #include "etcp.h"
 #include "conn_mgr.h"
+#include "db_sync.h"
 #include "stcp_server.h"
 #include "control_server.h"
 #include "msg_transport.h"
@@ -179,6 +180,9 @@ static int instance_init_common(struct UTUN_INSTANCE* instance, struct UASYNC* u
         return -1;
     }
 
+    // db_sync — распределённая таблица с репликацией (после etcp_router)
+    db_sync_init(instance);
+
     // Bind DATA handler via etcp_router (after etcp_router_init)
     if (routing_bind(instance) != 0) {
         DEBUG_ERROR(DEBUG_CATEGORY_ROUTING, "Failed to bind DATA via etcp_router");
@@ -417,6 +421,9 @@ void utun_instance_destroy(struct UTUN_INSTANCE *instance) {
         nat_transport_destroy(instance);
     }
 
+    // Cleanup db_sync (before etcp_router_destroy)
+    db_sync_destroy(instance);
+
     // Cleanup etcp_router
     etcp_router_destroy(instance);