Zone matrix: what the rules do between zones

internal/matrix walks each pair's rules in order, as nftables would, for
new connections: zone → zone (forward), zone → the firewall (input) and
back (output), with the built-ins that act on new connections. A rule
for the whole pair decides it; one for part of its traffic (addresses,
services, times, rates, a quota) is an exception; the rest falls to the
policy. Rules whose addresses all lie in networks connected to other
zones are left out of a pair. GET /matrix (with ?changeset, pending
changes), hc matrix [FROM TO], and a Matrix page whose cells open their
rules.

e2e: 166 checks, among them the matrix of the maintainer's imported
ruleset.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/routes.go

@@ -63,6 +63,7 @@ func (s *Server) routes() {
 	m.HandleFunc("DELETE "+p+"/{kind}/{ref}", s.authed(s.deleteObject))
 	m.HandleFunc("POST "+p+"/{kind}/{ref}/move", s.authed(s.moveObject))
 	m.HandleFunc("GET "+p+"/ruleset", s.authed(s.ruleset))
+	m.HandleFunc("GET "+p+"/matrix", s.authed(s.zoneMatrix))
 	m.HandleFunc("GET "+p+"/history", s.authed(s.listHistory))
 	m.HandleFunc("GET "+p+"/history/{id}", s.authed(s.getHistory))
 	m.HandleFunc("POST "+p+"/history/{id}/revert", s.authed(s.revertHistory))