feat: implement handle_config_request(), fetch_config_from_primary(), handle_controller_join()

- handle_config_request(): primary-side handler sends up-to-date flag or
  version_tag; SHA-256 integrity check guards against in-place file changes;
  sha256/bytes fields left NULL pending Task 11 typemap shims
- fetch_config_from_primary(): standby fetch with exponential backoff retry
  (20 attempts, 500ms..5s); falls back to saved config via load_primary_config();
  do_one_config_fetch() stubbed (-ENOSYS) until Task 11 wires capnp over SSL
- handle_controller_join(): registers standby endpoint in ha.standby_endpoints
  via zarray_store() for OP_upgradeConfig fan-out; sends success reply
- Moved load_primary_config() from myconf.c to config_repl.c so the unit test
  binary (which links config_repl.c but not myconf.c) can resolve it

src/controller/myconf.c

@@ -152,119 +152,6 @@ cluster_config_t* get_default_conf(void* cl)
     return cfg;
 }
 
-/* ── load_primary_config ────────────────────────── */
-
-int load_primary_config(cluster_t *c)
-{
-    myconf_t *myconf = c->myconf;
-
-    /* Build conf dir path: <workdir>/<name> */
-    char conf_dir[4096];
-    snprintf(conf_dir, sizeof(conf_dir), "%s/%s", myconf->workdir, myconf->name);
-
-    /* Resolve conf/current → versioned filename */
-    char fname[256] = {0};
-    int rc = conf_read_current_filename(conf_dir, fname, sizeof(fname));
-    if (rc != 0) {
-        ERROR("Primary has no config at '%s/conf/current' (rc=%d) — "
-              "provision the config before starting",
-              conf_dir, rc);
-        return -ENOENT;
-    }
-
-    /* Heap-allocate conffile so it survives past this stack frame */
-    free(myconf->conffile);
-    myconf->conffile = NULL;
-    if (asprintf(&myconf->conffile, "%s/conf/%s", conf_dir, fname) < 0)
-        return -ENOMEM;
-
-    /* Read raw bytes and check size */
-    uint8_t *bytes = NULL;
-    size_t   blen  = 0;
-    rc = conf_read_raw(myconf->conffile, &bytes, &blen);
-    if (rc != 0) {
-        ERROR("Primary config '%s' unreadable: %d", myconf->conffile, rc);
-        free(myconf->conffile);
-        myconf->conffile = NULL;
-        return rc;
-    }
-
-    /* Compute and cache SHA-256 */
-    SHA256(bytes, blen, myconf->config_sha256);
-    uint64_t tag;
-    memcpy(&tag, myconf->config_sha256, 8);
-    myconf->config_version_tag = be64toh(tag);
-
-    /* Free any prior decoded config before overwriting the pointer */
-    if (myconf->cluster_config) {
-        free_ClusterConfig(myconf->cluster_config);
-        free(myconf->cluster_config);
-        myconf->cluster_config = NULL;
-    }
-
-    /* Decode Cap'n Proto directly into myconf->cluster_config */
-    rc = load_cluster_config_from_file(myconf->conffile, &myconf->cluster_config);
-    if (rc != 0) {
-        ERROR("Primary config '%s' failed Cap'n Proto decode: %d",
-              myconf->conffile, rc);
-        free(bytes);
-        free(myconf->conffile);
-        myconf->conffile = NULL;
-        return rc;
-    }
-
-    if (myconf->cluster_config == NULL) {
-        ERROR("Primary config '%s' decoded to NULL", myconf->conffile);
-        free(bytes);
-        free(myconf->conffile);
-        myconf->conffile = NULL;
-        return -EINVAL;
-    }
-
-    free(bytes);
-
-    fill_default_cluster_config(myconf->cluster_config);
-
-    /* Check for reserved lost_and_found name */
-    if (config_contains_reserved_name(myconf->cluster_config)) {
-        ERROR("Config '%s' contains reserved name 'lost_and_found'",
-              myconf->conffile);
-        free_ClusterConfig(myconf->cluster_config);
-        free(myconf->cluster_config);
-        myconf->cluster_config = NULL;
-        free(myconf->conffile);
-        myconf->conffile = NULL;
-        return -EINVAL;
-    }
-
-    /* Default generation to 1 if not set */
-    if (myconf->cluster_config->config_generation == 0)
-        myconf->cluster_config->config_generation = 1;
-    myconf->config_generation = myconf->cluster_config->config_generation;
-
-    /* Check staleness */
-    myconf->conf_stale = conf_check_stale(conf_dir, myconf->conf_stale_timeout);
-    if (myconf->conf_stale)
-        WARN("Primary config appears stale (age > %lds)",
-             (long)myconf->conf_stale_timeout);
-
-    INFO("Primary config loaded: tag=%016" PRIx64 " gen=%" PRIu64,
-         myconf->config_version_tag, myconf->config_generation);
-    return 0;
-}
-
-/* ── fetch_config_from_primary ──────────────────── */
-
-int fetch_config_from_primary(cluster_t *c)
-{
-    (void)c;
-    /* Task 9: full implementation — connect to primary, send OP_replConfig,
-     * receive blob, verify SHA-256, call conf_save_config(), decode into
-     * myconf->cluster_config. */
-    ERROR("fetch_config_from_primary: not yet implemented (Task 9)");
-    return -ENOSYS;
-}
-
 /* ── myconf_fini ────────────────────────────────── */
 
 void myconf_fini(myconf_t *myconf)