Add PostgreSQL promotion database gate

ocf/loxthelion/managed-container.d/applications/postgresql/promote.sh

@@ -29,6 +29,11 @@ mc_pg_promote_database_shadow()
     if [ "${rc}" -ne 0 ]; then
         ocf_log warn \
             "managed-containerd promote.database shadow unavailable rc=${rc}"
+
+        if [ "${MC_PROMOTE_DATABASE_GATE:-false}" = true ]; then
+            return 1
+        fi
+
         return 0
     fi
 
@@ -50,10 +55,12 @@ if (
     else
         ocf_log err \
             "managed-containerd promote.database shadow MISMATCH response=${response}"
+
+        if [ "${MC_PROMOTE_DATABASE_GATE:-false}" = true ]; then
+            return 1
+        fi
     fi
 
-    # Shadow-only milestone: daemon disagreement must not alter the
-    # authoritative native promotion result yet.
     return 0
 }
 
@@ -117,9 +124,13 @@ managed_promote()
         "Promoting PostgreSQL standby inside ${CONTAINER_NAME}"
 
     # Independent managed-containerd promotion preflight.
-    # Shadow-only for now: disagreement is logged but does not block
-    # the authoritative native PostgreSQL promotion.
-    mc_pg_promote_database_shadow
+    # Shadow-only by default; when promote_database_gate=true,
+    # daemon disagreement or transport failure denies native promotion.
+    if ! mc_pg_promote_database_shadow; then
+        ocf_exit_reason \
+            "Promotion database gate rejected native PostgreSQL promotion"
+        return "${OCF_ERR_GENERIC}"
+    fi
 
     if ! pg_command '
         BINDIR="$(pg_config --bindir)" || exit 1