feat(webui): test coverage and CI gate (#436)

Add consolidated MVP route/read-only tests, path-filter helpers, and
scripts/test-webui plus scripts/ci-webui-check for Jenkins path-filtered
runs on PRs touching web UI surfaces.

Closes #436

scripts/test-webui

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -euo pipefail
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+repo_root="$(cd "$script_dir/.." && pwd)"
+cd "$repo_root"
+
+python_bin="${WEBUI_TEST_PYTHON:-python3}"
+if [[ -x "$repo_root/venv/bin/python" ]]; then
+  python_bin="$repo_root/venv/bin/python"
+fi
+
+pattern="${WEBUI_TEST_PATTERN:-test_webui_*.py}"
+exec "$python_bin" -m unittest discover -s tests -p "$pattern" "$@"