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)

scripts/ray-join.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Join the Ray cluster as an external worker.
+#
+# The Ray head's GCS port must be reachable from this machine.
+# Set RAY_HEAD_ADDRESS or pass it as the first argument.
+#
+# Usage:
+#   ./scripts/ray-join.sh                          # uses RAY_HEAD_ADDRESS env
+#   ./scripts/ray-join.sh 192.168.100.50:6379      # explicit address
+#   RAY_HEAD_ADDRESS=192.168.100.50:6379 ./scripts/ray-join.sh
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
+COMFYUI_DIR="$PROJECT_DIR/ComfyUI"
+
+RAY_HEAD="${1:-${RAY_HEAD_ADDRESS:-}}"
+
+if [[ -z "$RAY_HEAD" ]]; then
+    echo "ERROR: Ray head address required."
+    echo "Usage: $0 <ray-head-ip>:<port>"
+    echo "   or: RAY_HEAD_ADDRESS=<ip>:<port> $0"
+    exit 1
+fi
+
+# Activate ComfyUI venv (where Ray is installed)
+# shellcheck disable=SC1091
+source "$COMFYUI_DIR/.venv/bin/activate"
+
+# Stop any existing Ray worker on this machine
+ray stop --force 2>/dev/null || true
+
+echo "Joining Ray cluster at $RAY_HEAD..."
+
+ray start \
+    --address="$RAY_HEAD" \
+    --num-cpus=16 \
+    --num-gpus=1 \
+    --resources='{"3d_gen": 1, "rtx4070": 1}' \
+    --node-name=desktop
+
+echo ""
+echo "Desktop joined Ray cluster. Verify with: ray status"
+echo "To disconnect: ray stop"