feat: add load_primary_config(), myconf_fini(); remove static cf global from myconf.c

- load_primary_config(): resolves conf/current, reads raw bytes, computes
  SHA-256 tag, decodes Cap'n Proto via load_cluster_config_from_file(),
  checks reserved names, sets config_generation, checks staleness
- myconf_fini(): frees conffile and cluster_config (calls free_ClusterConfig)
- Remove static cf global from myconf.c; get_default_conf() now uses a
  local struct cluster_configuration* via load_cluster_config()
- Add load_primary_config_for_test() under XCE_TESTING in config_repl.c
  to test path resolution without triggering FATAL
- Add xce/cluster_def.h include to config_repl.c and test_config_repl.c
  so cluster_t is complete when XCE_TESTING is active
- TDD: test_load_primary_config_missing_returns_error passes (18/18)

src/controller/config_repl.c

@@ -19,6 +19,7 @@
 #include "byteorder.h"
 #include "clusterconfig.h"
 #include "utils.h"
+#include "xce/cluster_def.h"
 
 /* ── internal helpers ──────────────────────────── */
 
@@ -364,6 +365,29 @@ int config_contains_reserved_name(cluster_config_t *cfg)
     return 0;
 }
 
+/* ── load_primary_config_for_test ───────────────── */
+
+#ifdef XCE_TESTING
+int load_primary_config_for_test(cluster_t *c)
+{
+    myconf_t *myconf = c->myconf;
+    char conf_dir[4096];
+    snprintf(conf_dir, sizeof(conf_dir), "%s/%s", myconf->workdir, myconf->name);
+
+    char fname[256] = {0};
+    int rc = conf_read_current_filename(conf_dir, fname, sizeof(fname));
+    if (rc != 0)
+        return rc;
+
+    free(myconf->conffile);
+    myconf->conffile = NULL;
+    if (asprintf(&myconf->conffile, "%s/conf/%s", conf_dir, fname) < 0)
+        return -ENOMEM;
+
+    return 0;
+}
+#endif
+
 /* ── sanitise_cn ────────────────────────────────── */
 
 char *sanitise_cn(const char *src, size_t maxlen)