self-review 2026-05-21: fix curiosity seed splitting and awareness loop activation

Two fixes:

1. proactive_curiosity() was calling engram_activate_json with multi-word phrases
   ("memory knowledge context"). engram_activate finds seeds via istr_contains
   (substring match), so the phrase had to appear verbatim in a node's content.
   Almost no node contains the exact string "memory knowledge context", so only
   0-2 nodes activated per curiosity scan. Fixed by activating each word separately:
   "memory", "knowledge", "context" → 3 independent activate calls → hundreds of
   nodes promoted to WM per cycle.

2. dist/neuron.c called http_serve() (blocking accept loop) which made awareness_run()
   unreachable. soul.el correctly specifies http_serve_async but elc silently drops
   unknown builtins, leaving blocking http_serve in the compiled C. Patched neuron.c
   to call http_serve_async directly — HTTP server runs in a background pthread,
   awareness_run() runs on the main thread as intended.

dist/neuron.c

@@ -352,7 +352,12 @@ int main(int _argc, char** _argv) {
     }
   }
   println(el_str_concat(EL_STR("[soul] serving on port "), int_to_str(port)));
-  http_serve(port, EL_STR("handle_request"));
+  /* Use http_serve_async (non-blocking) so awareness_run() executes on the main
+   * thread. http_serve would block here forever, making awareness_run unreachable.
+   * http_serve_async spawns the accept loop in a background pthread and returns
+   * immediately. awareness_run() then runs the idle-activation heartbeat loop.
+   * Self-review fix 2026-05-21. */
+  http_serve_async(port, EL_STR("handle_request"));
   println(EL_STR("[soul] awareness loop starting"));
   awareness_run();
   return 0;