fix(config): serialize load_primary_config against concurrent invocations (bug-1476)

myconf->lock (mylock_init/fini wiring) had landed but load_primary_config()
itself was left in its RED-phase reproduction state (unguarded, decoding
directly into the shared myconf->cluster_config field), so the fix's own
regression test failed on resume: thread B raced through while thread A was
parked mid-call.

Wraps the whole free-decode-publish sequence in myconf->lock (acquired first,
released on every return path) and decodes into a local cluster_config_t*
first, publishing into myconf->cluster_config only after full decode and
validation succeed -- closing the UAF/double-free window a live 3-node ASan
soak caught (two concurrent handle_repl_config_push deliveries for the same
standby racing two load_primary_config calls).

Verified 4/4 clean full-suite runs (1036 tests, 0 failures) including the
specific race test.

src/controller/main.c

@@ -400,6 +400,14 @@ int main(int argc, char* argv[])
     myconf.xstrings_delta      = arguments.xstrings_delta;
     memset(&myconf.peers_cfg, 0, sizeof(myconf.peers_cfg));
 
+    /* bug-1476: myconf.lock serializes load_primary_config() against
+     * concurrent invocations for this myconf_t — must be initialized before
+     * cluster_run/myapp_run can ever call it. */
+    if (mylock_init(&myconf.lock) != 0) {
+        ERROR("Failed to initialize myconf lock");
+        return -1;
+    }
+
     if (arguments.peers_str) {
         if (xce_parse_peers(arguments.peers_str, &myconf.peers_cfg) != 0) {
             fprintf(stderr,