Add golden test data for via exit route steering and fix via exit grant compilation to match Tailscale SaaS behavior. Includes MapResponse golden tests for via grant route steering verification.
Updates #2180
Add routable_ips and approved_routes fields to the node topology
definitions in all golden test files. These represent the subnet
routes actually advertised by nodes on the Tailscale SaaS network
during data capture:
Routes topology (92 files, 6 router nodes):
big-router: 10.0.0.0/8
subnet-router: 10.33.0.0/16
ha-router1: 192.168.1.0/24
ha-router2: 192.168.1.0/24
multi-router: 172.16.0.0/24
exit-node: 0.0.0.0/0, ::/0
ACL topology (199 files, 1 router node):
subnet-router: 10.33.0.0/16
Grants topology (203 files, 1 router node):
subnet-router: 10.33.0.0/16
The route assignments were deduced from the golden data by analyzing
which router nodes receive FilterRules for which destination CIDRs
across all test files, and cross-referenced with the MTS setup
script (setup_grant_nodes.sh).
Updates #2180
Replace 8,286 lines of inline Go test expectations with 92 JSON golden files captured from Tailscale SaaS. The data-driven test driver validates route filtering, auto-approval, HA routing, and exit node behavior against real Tailscale output.
Updates #2180
Replace 9,937 lines of inline Go test expectations with 215 JSON golden files captured from Tailscale SaaS. The new data-driven test driver compares headscale's filter compilation output against real Tailscale behavior for each node in an 8-node topology.
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
