Replace no-send stub with real WAL entry transmission via
xce_wal_batch_req_raw. For each non-catch-up registered standby,
serialize the entry header+payload into a wal_catchup_entry_t
and enqueue. Keep the MAX_PENDING_ACKS eviction guard.
5 new tests: no-standbys, one-standby-send, skip-catch-up,
evict-overloaded, send-failure-continues. Controller suite green.
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>