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

webui/ci_paths.py

@@ -0,0 +1,20 @@
+"""Path filters for web UI CI gating (#436)."""
+
+from __future__ import annotations
+
+import re
+from collections.abc import Iterable
+
+_WEBUI_TOUCH_RE = re.compile(
+    r"^(?:webui/|tests/test_webui_|docs/webui|scripts/(?:run-webui|test-webui|ci-webui-check)$)"
+)
+
+
+def touches_webui_surface(path: str) -> bool:
+    """Return True when *path* is a web UI surface file."""
+    return bool(_WEBUI_TOUCH_RE.match(path.strip()))
+
+
+def should_run_webui_ci(changed_paths: Iterable[str]) -> bool:
+    """Return True when any changed path should trigger the web UI test suite."""
+    return any(touches_webui_surface(path) for path in changed_paths)