test(ha-commit-engine): RED integration tests for ACK feed and sync-append (task 5.1)

Tests 30-34: wired repl_on_ack feeds engine, membership mutators
trigger re-evaluation, per-entry sync-append contract (stale-ACK
rejection, committed_lsn unmoved on timeout, n_peers=1 replaces
-ENODEV). test_repl_majority walAck cases rewired to per-LSN
semantics (configAck byte-identical). Sanctioned scaffolding:
entry_lsn param on repl_wait_majority_ack (legacy body byte-identical,
callers pass 0), inert repl_set_commit_engine stub. 9 RED failures;
baseline signatures unchanged. LSN-0 edge documented for 5.2/5.3.

src/controller/persist.c

@@ -1029,7 +1029,10 @@ int persist_wal_sync_append(persist_t* p, uint32_t type,
     if (!has_standbys) {
         sync_err = -ENODEV;
     } else {
-        sync_err = repl_wait_majority_ack(&p->repl, p->config.sync_timeout_ms,
+        /* entry_lsn = 0: mechanical signature update only (ha-commit-engine
+         * task 5.1) — the legacy body ignores it. Task 5.3 passes
+         * written_lsn so the wired engine evaluates per-entry majority. */
+        sync_err = repl_wait_majority_ack(&p->repl, 0, p->config.sync_timeout_ms,
                                           (uint8_t)OPCode_walAck);
         if (sync_err == 0)
             atomic_store_explicit(&p->committed_lsn, written_lsn, memory_order_release);