Add versioned NeRD reference assets v1

Append an isolated example-resource bundle of four exact original files. Robot assets and Apache-2.0 license match NVlabs/neural-robot-dynamics@476dc67fccc6a99be293bf611f897b1c06f13e30. Existing data/model releases and asset hashes are unchanged.

demo/nerd/reference_assets/v1/README.md

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+# NeRD reference assets v1
+
+This independent example-resource bundle contains the exact four files formerly
+packaged under `embodichain/data/nerd`: two robot sources, the original upstream
+Apache2 license and the EmbodiChain attribution. It contains no trained weights,
+trajectory data or simulator binaries. The model and dataset releases in other
+Hugging Face repositories are unchanged.
+
+Robot sources and `LICENSE.md` match NVlabs/neural-robot-dynamics commit
+`476dc67fccc6a99be293bf611f897b1c06f13e30` byte-for-byte. `ATTRIBUTION.md` preserves the EmbodiChain provenance
+and interpretation notes without rewriting them. See `manifest.json` for every
+original byte count/SHA256 and the complete archive identity.
+
+`reference_assets.zip` stores a root `nerd_reference_assets/` directory entry
+before its four files. Entry order,1980timestamp,Unix modes and uncompressed ZIP
+encoding are deterministic. Downloaders must pin one immutable Hub revision,
+verify archive and member SHA256, reject traversal/absolute/duplicate/symlink or
+unexpected entries, and verify extracted files before using them. The associated
+NeRD example prepares these resources explicitly rather than requiring a core
+SDK data package or changing global download roots.
+
+Published model asset hashes remain:
+
+- CartPole: `f31276531c03050a3ac3a3e24443899f38a4424586db17140978383433dec237`
+- Ant: `23e9a720465a71fde3fd9fd2d5a18f8c11ec642f3dca8921c66cb4e169421fa7`
+
+These hashes identify the original robot bytes. They do not establish identical
+physics across importer profiles or solver versions; model/data deployment
+manifests retain their own physical signatures.

demo/nerd/reference_assets/v1/manifest.json

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+{
+  "archive": {
+    "compression": "stored",
+    "directory_entries": [
+      "nerd_reference_assets/"
+    ],
+    "filename": "reference_assets.zip",
+    "format": "zip",
+    "root": "nerd_reference_assets",
+    "sha256": "008d90d395422be81f8bbd9707fc05fafd358b44794b29ff0f6158a75cd1da22",
+    "size": 19269,
+    "timestamp": [
+      1980,
+      1,
+      1,
+      0,
+      0,
+      0
+    ]
+  },
+  "bundle": "nerd-reference-assets",
+  "embodichain_source_revision": "60425caa4308a44a9b4064470de148a4a05806ca",
+  "files": {
+    "ATTRIBUTION.md": {
+      "path": "nerd_reference_assets/ATTRIBUTION.md",
+      "sha256": "4d86dc2651a4e24903162e8bac2a96122952d49d91c7ffb52a7fa28119438ca5",
+      "size": 1201,
+      "source": "DexForce/EmbodiChain attribution"
+    },
+    "LICENSE.md": {
+      "path": "nerd_reference_assets/LICENSE.md",
+      "sha256": "59899c6091b540582ed617e8eeaac4919dc985ccfc35459ee9752b699be5205b",
+      "size": 10172,
+      "source": "NVlabs/neural-robot-dynamics@476dc67fccc6a99be293bf611f897b1c06f13e30:LICENSE.md"
+    },
+    "ant.xml": {
+      "path": "nerd_reference_assets/ant.xml",
+      "sha256": "23e9a720465a71fde3fd9fd2d5a18f8c11ec642f3dca8921c66cb4e169421fa7",
+      "size": 5231,
+      "source": "NVlabs/neural-robot-dynamics@476dc67fccc6a99be293bf611f897b1c06f13e30:envs/newton_envs/assets/ant.xml"
+    },
+    "cartpole_single.urdf": {
+      "path": "nerd_reference_assets/cartpole_single.urdf",
+      "sha256": "f31276531c03050a3ac3a3e24443899f38a4424586db17140978383433dec237",
+      "size": 1941,
+      "source": "NVlabs/neural-robot-dynamics@476dc67fccc6a99be293bf611f897b1c06f13e30:envs/newton_envs/assets/cartpole_single.urdf"
+    }
+  },
+  "huggingface": {
+    "path": "demo/nerd/reference_assets/v1",
+    "repo_id": "DexForceAI/embodichain_data",
+    "repo_type": "dataset"
+  },
+  "license": "Apache-2.0",
+  "published_model_asset_sha256": {
+    "ant": "23e9a720465a71fde3fd9fd2d5a18f8c11ec642f3dca8921c66cb4e169421fa7",
+    "cartpole": "f31276531c03050a3ac3a3e24443899f38a4424586db17140978383433dec237"
+  },
+  "schema_version": 1,
+  "upstream": {
+    "repository": "NVlabs/neural-robot-dynamics",
+    "revision": "476dc67fccc6a99be293bf611f897b1c06f13e30",
+    "url": "https://github.com/NVlabs/neural-robot-dynamics/tree/476dc67fccc6a99be293bf611f897b1c06f13e30"
+  },
+  "version": "v1"
+}

demo/nerd/reference_assets/v1/reference_assets.zip

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+version https://git-lfs.github.com/spec/v1
+oid sha256:008d90d395422be81f8bbd9707fc05fafd358b44794b29ff0f6158a75cd1da22
+size 19269