Backport #38074
## Summary
Fixes#38062.
Private repositories with a code unit configured for **anonymous read
access** (Settings → Public Access → Code: anonymous view) could not be
cloned without credentials. The git HTTP auth gate (`httpBase`) only
bypassed authentication for non-private repos, ignoring the per-unit
anonymous access setting entirely.
- Check anonymous permissions via
`access_model.GetDoerRepoPermission(ctx, repo, nil)` + `CanAccess`
before requiring auth on pull operations, so the per-unit
`AnonymousAccessMode` is respected through the existing permission model
- This also correctly handles `setting.Repository.ForcePrivate` (which
the naive direct-field check would have missed)
- Push (receive-pack) and `RequireSignInViewStrict` continue to require
credentials as before
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
