Install and inventory user-licensed DTU predictor archives

[iskandr]

Goal

Add a safe helper for NetMHC, NetMHCpan, NetMHCIIpan, NetMHCcons, NetMHCstabpan, and NetChop archives that a user has personally obtained from DTU.

Why --accept-license alone is insufficient

DTU does not expose an anonymous license-gated archive URL. Its official sw_request form requires the licensee's name, position, institutional email, and affiliation; acceptance executes an identity- and institution-bound academic license, and DTU emails a private download link. mhctools must not impersonate the licensee, submit personal details, or treat a boolean flag as equivalent to that registration.

Example official request page:
https://services.healthtech.dtu.dk/cgi-bin/sw_request?software=netMHCpan&version=4.2&packageversion=4.2e&platform=Linux

Proposed interface

# User first completes DTU's official form and downloads the archive.
mhctools install netmhcpan /path/to/netMHCpan-4.2e.Linux.tar.gz
mhctools ls netmhcpan

Acceptance criteria:

1. Never submit the DTU registration form or persist name/email/affiliation.
2. Validate the selected tool, platform, version, archive layout, and executable before installation.
3. Install atomically under MHCTOOLS_DATA_DIR without modifying upstream files unnecessarily.
4. Record archive checksum, requested tool/version, source/request URL, install path, and manager=mhctools provenance.
5. Keep existing manually installed executables discoverable as manager=manual.
6. Add uninstall/update guidance without redistributing DTU binaries.
7. Document that commercial users must obtain the corresponding commercial license.

This follows the artifact-management design while respecting DTU's identity-bound licensing flow.