[ViPPET] Add model-download service to Docker Compose stack

[p-zak]

Summary

Add the model-download microservice (intel/model-download:2026.1.0-20260331-weekly) to the ViPPET Docker Compose stack as a long-running service.
This is the first step in replacing the legacy models container - both services coexist in this PR; the old one will be removed in a follow-up.

What changed

compose.yml - Added model-download service definition:

• Uses the pre-built intel/model-download image (no local build).
• Shares the ./shared/models/ volume with vippet so downloaded models are immediately visible to inference pipelines.
• Persists the Python venv (/opt/.venv) and uv package cache (/cache) on host-mounted volumes under shared/model-download/ to avoid re-downloading ~2 GB of plugin dependencies on every container restart.
• Enabled plugins: openvino, huggingface, ultralytics, geti (configurable via MODEL_DOWNLOAD_PLUGINS env var).
• Health check on /api/v1/health, restart policy on-failure:5.

ui/nginx.conf - Added reverse proxy location /model-download/ → http://model-download:8000/api/v1/ so the UI can reach the service through the same origin (no CORS issues). Extended timeouts (300 s) and client_max_body_size 5G for large model uploads.

ui/vite.config.ts - Added dev proxy /model-download → http://localhost:8000 with path rewrite to /api/v1 for local development.

Makefile - Additive changes only:

• env-setup creates shared/model-download/{venv,cache} directories.
• Added shell-model-download target.
• stop and clean targets now include the new service/directories.
• All legacy models targets (install-models-*, build-models, shell-models) are preserved unchanged.

Routing

Browser → :80/model-download/* → nginx → model-download:8000/api/v1/*

How to test

make build && make run
# Wait for model-download to become healthy (~1-2 min first run, seconds on subsequent runs)
docker ps --filter name=model-download
curl http://localhost:80/model-download/health   # → {"status":"ok"}
curl http://localhost:80/model-download/plugins   # → list of available plugins