Initial snapshot: hand motion pipeline (Dyn-HaMR + dex-retargeting + SPIDER)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

third_party/spider/docs/workflows/workflow-hdmi.md

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+# Workflow: HDMI (Humanoid-Object Interaction)
+
+The HDMI workflow integrates SPIDER with [HDMI (Humanoid Manipulation)](https://github.com/lecar-lab/hdmi) framework for humanoid robot manipulation with downstream sim2real RL training.
+
+## Prerequisites
+
+### Install HDMI Environment
+
+Follow the [official HDMI installation guide](https://github.com/lecar-lab/hdmi):
+
+```bash
+# Clone HDMI repository
+git clone https://github.com/lecar-lab/hdmi.git
+cd hdmi
+
+# Install with uv (recommended)
+uv sync
+
+# Install SPIDER into HDMI environment
+uv pip install --no-deps -e /path/to/spider
+```
+
+## Running HDMI Workflow
+
+### Basic Example
+
+```bash
+cd /path/to/spider
+
+# Run with default config (G1 humanoid, suitcase task)
+python examples/run_hdmi.py
+# OR refer to
+./examples/run_hdmi.sh
+```
+
+### Configuration Options
+
+You can enable `mjlab` native viewer by setting `viewer` to `hdmi`.
+
+## Train RL
+
+Write the motion as one HDMI reference motion by running the following command:
+
+```bash
+python examples/postprocess/read_to_hdmi.py
+```