refactor: reorganize directory structure and remove hardcoded paths

Move comfyui and vllm out of models/ directory to top level for better
organization. Replace all hardcoded /workspace paths with relative paths
to make the configuration portable across different environments.

Changes:
- Move models/comfyui/ → comfyui/
- Move models/vllm/ → vllm/
- Remove models/ directory (empty)
- Update arty.yml: replace /workspace with environment variables
- Update supervisord.conf: use relative paths from /workspace/ai
- Update all script references to use new paths
- Maintain TQDM_DISABLE=1 to fix BrokenPipeError

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

vllm/requirements.txt

@@ -0,0 +1,4 @@
+# vLLM Text Generation Service Dependencies
+
+# vLLM engine (will install compatible torch, transformers, etc.)
+vllm==0.6.4.post1