fix: harden UCE runtime and starter

site/doc/pages/request_query_path.txt

@@ -0,0 +1,27 @@
+:title
+request_query_path
+
+:sig
+String request_query_path(Request& context, String default_path = "index")
+
+:see
+request_query_route
+request_context_params
+route_path_sanitize
+route_path_is_safe
+parse_query
+
+:content
+Returns the first keyless query-string segment as a sanitized route path.
+
+For a request such as `/?workspace/projects&theme=dark`, this returns `workspace/projects`.
+
+When no keyless route is supplied, the result is `default_path`. When unsafe route input is supplied, the result is an empty string. Unsafe route input includes `.` or `..` segments, empty interior segments, backslashes, dots in filenames, or any character outside ASCII letters, digits, `_`, and `-`.
+
+```cpp
+String route_path = request_query_path(context);
+if(route_path == "")
+    context.set_status(404, "Not Found");
+```
+
+The runtime-populated `context.params["ROUTE_PATH"]` uses the same sanitizer.