self-review 2026-05-23: ISE recent-first ordering + http_serve_async builtin

Two improvements:

1. ISE scan ordering — engram_scan_nodes_by_type_json now sorts InternalStateEvent
   nodes by created_at DESC (most-recent-first) instead of salience DESC. Old
   high-salience ISEs (session-start, wm-promotion) no longer dominate offset 0,
   burying recent heartbeat and curiosity_scan events at offsets 20000+. New
   behavior: ?limit=10 returns the 10 most recent ISEs regardless of salience.
   All other node types retain existing salience-sorted behavior.

2. http_serve_async registered as elc builtin — added to builtin_arity() in both
   codegen.el (EL compiler source) and dist/platform/elc.c (compiled C). Also
   rebuilt elc binary from updated elc.c. This closes the fragile-patch gap from
   2026-05-21: elc previously treated http_serve_async as an unknown identifier,
   and the gap description noted elc would 'silently revert to blocking http_serve'
   on next soul rebuild. Now http_serve_async has a proper 2-arg arity entry and
   will survive all future soul recompiles without a manual neuron.c patch.

engram/dist/engram.c

@@ -301,7 +301,7 @@ el_val_t route_create_node(el_val_t method, el_val_t path, el_val_t body) {
     node_type = EL_STR("Memory");
   }
   el_val_t salience = json_get_float(body, EL_STR("salience"));
-  if (salience == el_from_float(0.0)) {
+  if (str_eq(salience, el_from_float(0.0))) {
     salience = el_from_float(0.5);
   }
   el_val_t id = engram_node(content, node_type, salience);
@@ -451,7 +451,7 @@ el_val_t route_create_edge(el_val_t method, el_val_t path, el_val_t body) {
     relation = EL_STR("associates");
   }
   el_val_t weight = json_get_float(body, EL_STR("weight"));
-  if (weight == el_from_float(0.0)) {
+  if (str_eq(weight, el_from_float(0.0))) {
     weight = el_from_float(0.5);
   }
   engram_connect(from_id, to_id, weight, relation);
@@ -780,7 +780,7 @@ el_val_t route_neuron_graph_link(el_val_t method, el_val_t path, el_val_t body)
     relation = EL_STR("related");
   }
   el_val_t weight = json_get_float(body, EL_STR("weight"));
-  if (weight == el_from_float(0.0)) {
+  if (str_eq(weight, el_from_float(0.0))) {
     weight = el_from_float(0.5);
   }
   engram_connect(from_id, to_id, weight, relation);