feat(sim): VLABench benchmark integration

Add VLABench (language-conditioned manipulation with long-horizon
reasoning) as a new simulation benchmark, following the established
LIBERO/MetaWorld patterns.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/source/_toctree.yml

@@ -81,6 +81,8 @@
     title: Meta-World
   - local: envhub_isaaclab_arena
     title: NVIDIA IsaacLab Arena Environments
+  - local: vlabench
+    title: VLABench
   title: "Benchmarks"
 - sections:
   - local: introduction_processors