etcp: replace connections linked-list with indexed ll_queue, add state/ref_count lifecycle

- Remove ETCP_CONN.next linked-list, UTUN_INSTANCE.connections list/count
- Unified connections in single ll_queue indexed by peer_node_id (0=pending)
- struct conn_queue_entry { peer_node_id, conn* } for uniform queue data
- Connection lifecycle via etcp.c: create→pending, conn_ready→indexed, close→detach+deferred free
- Close split: phase1 detach from external world, phase2 deferred via uasync_call_soon
- etcp_conn_set_peer_node_id: reindex on ID change (WARN)
- etcp_conn_ref_take/free: blocking close until refcount returns to 0
- Remove chat_connections — use unified connections queue directly
- Update all iteration/search patterns across 40 files (src + tests + chatgui)

tests/test_socks_http_proxy.c

@@ -215,10 +215,15 @@ static char* make_cfg_client(void) {
 }
 
 static int conn_ready(struct UTUN_INSTANCE* inst) {
-    if (!inst) return 0;
-    for (struct ETCP_CONN* c = inst->connections; c; c = c->next)
+    if (!inst || !inst->connections) return 0;
+    struct ll_entry* entry = inst->connections->head;
+    while (entry) {
+        struct conn_queue_entry* ce = (struct conn_queue_entry*)entry->data;
+        struct ETCP_CONN* c = ce->conn;
         for (struct ETCP_LINK* l = c->links; l; l = l->next)
             if (l->initialized && c->crypto_ctx.initialized) return 1;
+        entry = entry->next;
+    }
     return 0;
 }