ipx-web uses Caddy's global metrics option (#381)

The browser tests ran Debian's Caddy 2.6, which has no global metrics
option, so the Caddyfile nested it in servers, which production's 2.11
logs as deprecated at every start. The tests now run Caddy 2.11 from
Caddy's own repository (install.sh), the version the caddy:2 image has.

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

web/Caddyfile

@@ -14,11 +14,7 @@
 	admin off
 	auto_https off
 	# Requests, their times and upstream errors as Prometheus metrics, served below (#371).
-	# Nested in servers, which Caddy 2.11 calls deprecated, for the browser tests' Caddy, 2.6,
-	# which knows no other way; the global `metrics` option once both are 2.8 or later.
-	servers {
-		metrics
-	}
+	metrics
 	# Everything else Caddy logs, its errors among them, which carry the request too: the same
 	# filter as the access log's below.
 	log default {