fix: grant limited-org unit read access to authenticated non-members

[waterWang]

Problem

An organization set to Limited ("Visible only to authenticated users") hides the Packages, Code, and Projects tabs for signed-in non-members. Only the Repositories tab is shown. While Packages still loads if the URL is entered directly, Code and Projects return 404.

The same organization set to Public shows all tabs to everyone, including anonymous visitors.

Expected: limited visibility should show the same tabs as public, with the audience narrowed to authenticated users.

Root Cause

Organization.UnitPermission() in models/organization/org.go:

if org.Visibility.IsPublic() {
    return perm.AccessModeRead
}
return perm.AccessModeNone

A signed-in non-member has no teams in the org, so the first block (team check) is skipped. IsPublic() returns true only for VisibleTypePublic, so limited falls through to AccessModeNone.

This cascades to services/context/org.go where CanReadUnit() wraps UnitPermission(), and templates/org/menu.tmpl hides tabs when CanReadPackages etc. are false.

Fix

Add (doer != nil && org.Visibility.IsLimited()) to the read-access condition:

if org.Visibility.IsPublic() || (doer != nil && org.Visibility.IsLimited()) {
    return perm.AccessModeRead
}

limited orgs grant read access to authenticated users and deny it to anonymous visitors — matching the documented semantics of the visibility setting.

Fixes #38870

[dianaStr7]

That was fast, thank you :)

[wxiaoguang]

Thank you, please add a simple test.