feat(\db-tool\): introduce unified db-tool package with postgres harness and tests (T0-T8)

legacy/helper/posix-shell/pager_or_cat.sh

@@ -0,0 +1,8 @@
+pager_or_cat_init() {
+  # Pipe to pager only if stdout is a terminal, otherwise output directly
+  if [ -t 1 ]; then
+    PAGER_OR_CAT="${PAGER:-less}"
+  else
+    PAGER_OR_CAT=cat
+  fi
+}