Add marker to el elements _MAPPING

- Enables rx.el.marker and rx.el.svg.marker access
- Addresses PR feedback from @adhami3310
- Marker now properly available through el namespace only

Co-Authored-By: [email protected] <[email protected]>

Author: devin-ai-integration[bot]

reflex/components/el/elements/__init__.py

@@ -78,6 +78,7 @@
         "linear_gradient",
         "radial_gradient",
         "defs",
+        "marker",
     ],
     "metadata": [
         "base",