Require a token to scrape /metrics

The metrics endpoint fans out a gather to every connected host, so
anyone who could reach the controller could read cluster statistics and
put load on all hosts at will. Scraping now needs a user token holding
the new core.controller.metrics permission. The token is accepted via
Authorization: Bearer as well as X-Access-Token because Prometheus can
only send the former. Concurrent scrapes share one gather so hosts see
at most one metrics request at a time.

The three connection gauges in controller.ts now no-op before the
controller exists, like the other gauges there, so the endpoint can be
tested against the mock controller.

Closes #1009

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

packages/controller/controller.ts

@@ -101,6 +101,9 @@ void new lib.Gauge(
 	"clusterio_controller_websocket_active_connections",
 	"How many WebSocket connections are currently open to the controller",
 	{ callback: function(gauge:lib.Gauge) {
+		if (!controller) {
+			return;
+		}
 		gauge.set(controller.wsServer.activeConnectors.size);
 	}}
 );
@@ -109,6 +112,9 @@ void new lib.Gauge(
 	"clusterio_controller_active_hosts",
 	"How many hosts are currently connected to the controller",
 	{ callback: function(gauge:lib.Gauge) {
+		if (!controller) {
+			return;
+		}
 		gauge.set(controller.wsServer.hostConnections.size);
 	}}
 );
@@ -118,6 +124,9 @@ void new lib.Gauge(
 	"How many clients are currently connected to this controller",
 	{
 		labels: ["type"], callback: async function(gauge:lib.Gauge) {
+			if (!controller) {
+				return;
+			}
 			gauge.labels("host").set(controller.wsServer.hostConnections.size);
 			gauge.labels("control").set(controller.wsServer.controlConnections.size);
 		},