switch nextcloud to FPM + Nginx for better static file performance

Replace the all-in-one Apache image with nextcloud:33-fpm and an Nginx
sidecar that serves static assets directly with gzip compression and
cache headers, avoiding the prefork concurrency bottleneck.

caddy/Caddyfile

@@ -9,14 +9,10 @@
 }
 
 nextcloud.t-gstone.de {
-	encode zstd gzip
-	reverse_proxy nextcloud:80
+	reverse_proxy nextcloud-nginx:80
 
 	header Strict-Transport-Security "max-age=31536000; includeSubDomains; preload"
 
-	redir /.well-known/carddav /remote.php/dav/ 301
-	redir /.well-known/caldav /remote.php/dav/ 301
-
 	request_body {
 		max_size 10G
 	}