fix(cluster): close four-node PCM-X liveness campaign (#64)

Stabilize PCM-X queue ownership, transfer, retirement, visibility, and fail-closed handling across concurrent four-node writers. Add deterministic unit and TAP coverage for routing, dirty-image retention, queue drainage, data conservation, and injected buffer-flush failures. Restore cluster-disabled compilation and zero-finding cppcheck parity. Validation: t/400 228/228 PASS; fast-gate all jobs PASS.

Author: sqlrush

scripts/ci/run-cppcheck.sh

@@ -240,6 +240,8 @@ cppcheck \
   --xml --xml-version=2 \
   -I src/include \
   -DUSE_PGRAC_CLUSTER=1 \
+  '-DHEAPAM_SOURCE_PATH="src/backend/access/heap/heapam.c"' \
+  '-DTT_LOCAL_SOURCE_PATH="src/backend/cluster/cluster_tt_local.c"' \
   --quiet \
   "${CLUSTER_DIRS[@]}" \
   2> cppcheck.xml