feat(config-upgrade-snapshot): live config-upgrade soak infra + fix bug-1468/bug-1469 (task 8.6)

Build the live 3-node chaotic-multi-kill config-upgrade soak scenario
(run-ha-soak.sh --config-upgrade) required by Requirements 4.1, 4.3, 6.1,
6.4. This needed genuinely new client-side infrastructure: a hand-rolled
capnp send path for OP_upgradeConfig (the auto-generated encoder is a
no-op for its Data fields, worked around the same way
xce_replconfigpush_req_raw already does), plus cmd_hostctrl/cmd_upgradeconfig
CLI commands.

Building and running this live surfaced two real production bugs, both
fixed here:

- bug-1468: an unrelated prior commit inverted OPCode_upgradeConfig's
  primary/standby dispatch guard in cluster.c, making config upgrades
  unreachable from any network client.
- bug-1469: apply_committed_entry's WAL_CONFIG_MARKER case never called
  config_activate_committed(), so the node that originates a config
  upgrade never refreshed its own in-memory state as part of committing
  it. Killing that node before some later, unrelated event happened to
  refresh it left its checkpoint permanently stale -- the first live,
  empirical reproduction of bug-857's originally hypothesized failure
  mode. Fixed by activating before the marker-triggered checkpoint write,
  since checkpoint content is built from live runtime tables that only
  reflect the reload after activation runs.

A separate, narrower checkpoint divergence (bug-1471, not config-related)
remains open and still blocks a clean soak PASS -- task 8.6 stays
in-progress until it's resolved.

src/lib/client.c

@@ -778,6 +778,25 @@ int xcecli_hostctrl(xcecli_ctx_t c, xce_hostctrl_t* ctrlinfo)
     return rc;
 }
 
+int xcecli_upgradeconfig(xcecli_ctx_t c, const uint8_t *sha256,
+                         size_t sha256_len, const uint8_t *bytes,
+                         size_t bytes_len)
+{
+    api_ctx_t* ctx = (api_ctx_t*)c;
+    int        rc;
+
+    if ((ctx == NULL) || (sha256 == NULL) || (sha256_len == 0)
+        || (bytes == NULL) || (bytes_len == 0)) {
+        return -EINVAL;
+    }
+
+    rc = XCECLI_FAILOVER_CALL(ctx, /*is_write=*/true,
+                              xce_upgradeconfig(&(ctx->ctx), sha256,
+                                                sha256_len, bytes,
+                                                bytes_len));
+    return rc;
+}
+
 int xcecli_runtask(xcecli_ctx_t c, xce_taskrun_t* info)
 {
     api_ctx_t* ctx = (api_ctx_t*)c;