AppendToIPSet now adds both IPv4 and IPv6 addresses for nodes, matching Tailscale's FilterRule wire format where identity-based aliases (tags, users, groups, autogroups) resolve to both address families. Update ReduceFilterRules test expectations to include IPv6 entries.
Updates #2180
Introduce ResolvedAddresses type for structured IP set results. Refactor all Alias.Resolve() methods to return ResolvedAddresses instead of raw IPSets. Restrict identity-based aliases to matching address families, fix nil dereferences in partial resolution paths, and update test expectations for the new IP format (bare IPs, IP ranges instead of CIDR prefixes).
Updates #2180
Rename tailscale_compat_test.go to tailscale_acl_compat_test.go to make room for the grants compat test. Add 237 GRANT-*.json golden test files captured from Tailscale SaaS and a data-driven test driver that compares headscale's grant filter compilation against real Tailscale behavior.
Updates #2180
