chore(pusht): add 5090 repro docs and uv setup

setup_uv_pusht_5090.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "$0")" && pwd)"
+cd "$ROOT_DIR"
+
+export UV_CACHE_DIR="${UV_CACHE_DIR:-$ROOT_DIR/.uv-cache}"
+export UV_PYTHON_INSTALL_DIR="${UV_PYTHON_INSTALL_DIR:-$ROOT_DIR/.uv-python}"
+
+uv venv --python 3.9 .venv
+source .venv/bin/activate
+
+uv pip install --upgrade pip wheel setuptools==80.9.0
+uv pip install --python .venv/bin/python \
+  --index-url https://download.pytorch.org/whl/cu128 \
+  torch==2.8.0+cu128 torchvision==0.23.0+cu128 torchaudio==2.8.0+cu128
+uv pip install --python .venv/bin/python -r requirements-pusht-5090.txt
+uv pip install --python .venv/bin/python -e .
+
+echo "uv environment ready at $ROOT_DIR/.venv"