Implement SSH forwarding for Forgejo Git access

- Add nginx stream configuration on reverse-proxy to forward port 2222 to apps:22
- Update firewall rules to allow port 2222 for Git SSH access
- Configure Forgejo to use SSH_PORT = 2222 for Git operations
- Add comprehensive SSH forwarding research documentation
- Enable Git operations via git@git.geokkjer.eu:2222

Phase 1 implementation using nginx stream module complete.
Ready for testing and potential Phase 2 migration to HAProxy.

machines/grey-area/services/forgejo.nix

@@ -15,6 +15,7 @@
     server = {
       ROOT_URL = "http://apps:3000";
       SSH_DOMAIN = "git.geokkjer.eu";
+      SSH_PORT = 2222;
     };
     repository = {
       ENABLE_PUSH_CREATE_USER = true;