## Problem
Helm charts like Intel device plugins have download URLs on `github.com` but the chart index is served from `intel.github.io`. The merger rewrites all URLs through the proxy, constructing:
```
https://artifactapi/api/v1/remote/intel-helm/intel/helm-charts/releases/download/...
```
Which proxies to `https://intel.github.io/helm-charts/intel/helm-charts/releases/download/...` — a 404.
## Fix
Compare the download URL host against the remote's base URL host. If they differ, leave the URL as-is so helm downloads directly from the source. Same-host URLs are still rewritten through the proxy.
Also adds `BaseURL` to `MemberIndex` so the merger has the context it needs, and uses the correct `/local/` vs `/remote/` route prefix.
Reviewed-on: #56
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>
## Summary
- Virtual engine detects local members and generates indexes in-memory
- MemberIndex.RepoType drives correct URL prefix in merged output
- PyPI merger rewrites links to /api/v1/local/ or /api/v1/remote/ appropriately
- Includes local PyPI support (cherry-picked from #50)
## Test plan
- [x] Upload wheel to local PyPI → install from direct local URL
- [x] Create virtual with local + remote → install from virtual URL
- [x] Both paths produce correct absolute download URLs
Reviewed-on: #51
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>