fix(install): surface custom port in generic host clone/ls-remote error

[edenfunf]

Description

The two is_generic error branches in github_downloader render the bare host in the "For private repositories on {host}" hint, dropping any custom port. Users on Bitbucket Datacenter (or any self-hosted host on a non-default port) see a diagnostic that hides the very detail they need to verify their git credential helper against:

For private repositories on bitbucket.corp.com, configure SSH keys or a git credential helper.

instead of:

For private repositories on bitbucket.corp.com:7999, configure SSH keys or a git credential helper.

Both branches now route through AuthResolver.classify_host(...).display_name, so the generic path shares port rendering with the adjacent ADO and auth branches (which already used build_error_context → host_info.display_name). This also means any future refinement to HostInfo.display_name (e.g. default-port normalisation, tracked in #797) propagates to these two call sites for free.

Scope-limited per the issue: no new signatures, no schema impact; only the two host_name = dep_host or "..." lines change. The "the target host" fallback is kept for the (unreachable-today but defensive) dep_host=None case, mirroring the dep_ref.port if dep_ref else None guard already used at the neighbouring auth call sites.

Fixes #798

Type of change

• Bug fix
• New feature
• Documentation
• Maintenance / refactor

Testing

• Tested locally
• All existing tests pass
• Added tests for new functionality (if applicable)

New regression tests in tests/unit/test_generic_host_error_port.py cover both error branches with three shapes each: ssh custom port (Bitbucket DC 7999), https custom port (Bitbucket DC 7990), and a no-port control that guards against spurious : suffixes. Temporarily reverting the fix turns the four port-bearing assertions red with the exact bare-host string described in the issue, then green again once the fix is reapplied -- the tests bite on the regression they're named after.

Manual verification with ssh://git@bitbucket.nonexistent-host.example:7999/team/repo.git:

Failed to clone repository team/repo via SSH. ...
For private repositories on bitbucket.nonexistent-host.example:7999, configure SSH keys or a git credential helper.
APM delegates authentication to git for non-GitHub/ADO hosts.

pytest tests/unit -q → 4449 passed, 0 new failures. The three pre-existing failures in tests/test_github_downloader.py reproduce on origin/main without this patch and are unrelated.