ci: add dashboard-description lint

Checks every grafana dashboard panel/board description against a length
cap and a small keyword list (operator name, tracker-tag references) so
the descriptions just shortened don't regress. Wired into both CI and
pre-push, same as the other content lints.

scripts/pre-push

@@ -31,5 +31,13 @@ if ! sh "$repo_root/scripts/check-attribution-trailers.sh"; then
   exit 1
 fi
 
+echo "pre-push: running dashboard-description lint..." >&2
+# jq isn't a project dependency elsewhere in this repo, so the check script
+# assumes nothing about the caller's PATH — nix-shell it here instead.
+if ! nix shell nixpkgs#jq --command sh "$repo_root/scripts/check-dashboard-descriptions.sh"; then
+  echo "pre-push: dashboard-description lint FAILED — fix before pushing" >&2
+  exit 1
+fi
+
 echo "pre-push: lints passed ✓" >&2
 exit 0