feat: send_q backpressure + ll_queue on_get callback + consumer_ack flow control

etcp_router: ROUTER_MAX_SEND_Q_PACKETS=256, router_enqueue_send returns
error when send_q full, etcp_route_send propagates -1 on backpressure.

ll_queue: queue_set_on_get — deferred callback after each queue_data_get.
Replaces manual consumer_ack polling with queue-driven notification.

tcp_proxy_server: consumer_ack=1, write_on_get_cb triggers ACK on
each write_queue dequeue. Full backpressure chain:
  write_queue full → no dequeue → no ACK → sender stops → all queues pause
  write_queue drains → dequeue → on_get → ACK → sender resumes

src/proxy/tcp_proxy_server.c

@@ -100,9 +100,16 @@ static void send_error(struct tcp_proxy_server_conn* rc) {
 }
 
 // ====================================================================
-// Коллбэки tcp_io
+// Коллбэки tcp_io + очередь
 // ====================================================================
 
+static void write_on_get_cb(struct ll_queue* q, void* arg) {
+    (void)q;
+    struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;
+    struct UTUN_INSTANCE* inst = rc->ctx ? rc->ctx->inst : NULL;
+    if (inst) etcp_router_consumer_ack(inst, rc->peer_node_id, ETCP_ID_TCP_PROXY);
+}
+
 static void on_fin_cb(struct tcp_conn* tc, void* arg) {
     struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;
     if (write_pending(tc))
@@ -112,6 +119,7 @@ static void on_fin_cb(struct tcp_conn* tc, void* arg) {
 }
 
 static void on_flushed_cb(struct tcp_conn* tc, void* arg) {
+    (void)tc;
     struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;
     if (rc->cli_closed) { tcp_proxy_server_conn_free(rc); return; }
     send_close(rc);
@@ -168,7 +176,11 @@ static void read_queue_drain_cb(struct ll_queue* q, void* arg) {
     if (ret == 0) {
         queue_resume_callback(q);
     } else {
-        etcp_router_waiter_register(inst, rc->peer_node_id, &rc->pause_waiter, pause_resume_cb, rc);
+        struct ETCP_ROUTER_CONN* rconn = etcp_router_conn_get(inst, rc->peer_node_id, ETCP_ID_TCP_PROXY);
+        if (rconn && rconn->send_q)
+            queue_waiter_wait(rconn->send_q, &rc->pause_waiter, pause_resume_cb, rc);
+        else
+            etcp_router_waiter_register(inst, rc->peer_node_id, &rc->pause_waiter, pause_resume_cb, rc);
     }
 }
 
@@ -202,7 +214,12 @@ void tcp_proxy_server_conn_free(struct tcp_proxy_server_conn* rc) {
     if (rc->tc) { tcp_conn_destroy(rc->tc); rc->tc = NULL; }
     if (rc->close_timer) { uasync_cancel_timeout(rc->ua, rc->close_timer); rc->close_timer = NULL; }
     if (rc->diag_timer) { uasync_cancel_timeout(rc->ua, rc->diag_timer); rc->diag_timer = NULL; }
-    if (rc->ctx && rc->ctx->inst) etcp_router_waiter_cancel(rc->ctx->inst, rc->peer_node_id, &rc->pause_waiter);
+    if (rc->ctx && rc->ctx->inst) {
+        struct ETCP_ROUTER_CONN* rconn = etcp_router_conn_get(rc->ctx->inst, rc->peer_node_id, ETCP_ID_TCP_PROXY);
+        if (rconn && rconn->send_q) queue_waiter_cancel(rconn->send_q, &rc->pause_waiter);
+        else etcp_router_waiter_cancel(rc->ctx->inst, rc->peer_node_id, &rc->pause_waiter);
+    }
+    if (rc->tc) queue_set_on_get(rc->tc->write_queue, NULL, NULL);
     u_free(rc);
 }
 
@@ -254,6 +271,13 @@ int tcp_proxy_server_handle_connect(struct UTUN_INSTANCE* inst, struct ll_entry*
 
     rc->next = ctx->conns; ctx->conns = rc;
     rc->diag_timer = uasync_set_timeout(rc->ua, 10000, rc, diag_timer_cb, "tps_diag");
+
+    {
+        struct ETCP_ROUTER_CONN* rconn = etcp_router_conn_get(inst, src_node_id, ETCP_ID_TCP_PROXY);
+        if (rconn) rconn->consumer_ack = 1;
+    }
+    queue_set_on_get(rc->tc->write_queue, write_on_get_cb, rc);
+
     queue_dgram_free(entry); queue_entry_free(entry);
     return 0;
 }