Revert to port 2525 without authentication for internal mail relay

The STARTTLS port 2587 requires TLS certificate verification, but
Cloudron's internal mail relay uses a wildcard cert for *.due.ren
which doesn't match the hostname 'mail'. Port 2525 is the internal
plain SMTP relay that doesn't require authentication or TLS for
connections from within the same container network.

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

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

CloudronManifest.json

@@ -7,7 +7,7 @@
   "contactEmail": "contact@ente.io",
   "website": "https://ente.io",
   "tagline": "Open source, end-to-end encrypted photo backup",
-  "version": "0.3.8",
+  "version": "0.3.9",
   "upstreamVersion": "git-main",
   "healthCheckPath": "/health",
   "httpPort": 3080,