feat: scaffold avatar pipeline with ComfyUI driver, MLflow logging, and rclone promotion

- setup.sh: automated desktop env setup (ComfyUI, 3D-Pack, UniRig, Blender, Ray)
- ray-join.sh: join Ray cluster as external worker with 3d_gen resource label
- vrm_export.py: headless Blender GLB→VRM conversion script
- generate.py: ComfyUI API driver (submit workflow JSON, poll, download outputs)
- log_mlflow.py: REST-only MLflow experiment tracking (no SDK dependency)
- promote.py: rclone promotion of VRM files to gravenhollow S3
- CLI entry points: avatar-generate, avatar-promote
- workflows/ placeholder for ComfyUI exported workflow JSONs

Implements ADR-0063 (ComfyUI + TRELLIS + UniRig 3D avatar pipeline)

workflows/README.md

@@ -0,0 +1,9 @@
+# Workflow JSON files exported from ComfyUI go here.
+#
+# To export a workflow in API format:
+# 1. Open ComfyUI at http://localhost:8188
+# 2. Build your node graph (TRELLIS → mesh processing → UniRig → export)
+# 3. Click "Save (API Format)" or use Developer Mode → "Save API workflow"
+# 4. Save the JSON file to this directory
+#
+# The generate.py driver loads these and submits them to ComfyUI's /prompt API.