fix(ha-heartbeat-liveness): start primary heartbeat in COMMITTING phase (task 4.3)

Call ha_start_primary_heartbeat in raft_cb_become_leader when entering
CTRL_PRIMARY_COMMITTING so standbys receive NOPs during the committing
window. Fixes 60s stability: 0 false RDHUP events on standbys.

src/controller/ha.c

@@ -434,6 +434,12 @@ static void raft_cb_become_leader(void *ctx, uint64_t term)
 #else
         ha_send_ctrlhello_to_all_standbys(c);
 #endif
+        /* Start primary heartbeat immediately in COMMITTING so standbys receive
+         * NOP during the committing window and their liveness poll does not fire.
+         * ha_start_primary_heartbeat is also called in ha_promote_to_primary;
+         * the idempotency guard (role check at fn top) prevents double-arming. */
+        ha_start_primary_heartbeat(c);
+
         /* Arm committing timeout watchdog */
         committing_timeout_ctx_t *ct = calloc(1, sizeof(*ct));
         if (ct) {