Add backend transport timeouts and Mailcow-specific transport

Configure default server transport with connection timeouts and add insecure transport for Mailcow backend with self-signed certificates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

traefik.yml

@@ -35,3 +35,13 @@ providers:
   file:
     filename: /etc/traefik/dynamic.yml
     watch: true
+
+serversTransport:
+  forwardingTimeouts:
+    dialTimeout: 30s
+    responseHeaderTimeout: 0s
+    idleConnTimeout: 3600s
+
+serversTransports:
+  mailcow-transport:
+    insecureSkipVerify: true