fix: improve nginx template container matching for docker-gen 0.16.x

Use multiple fallback methods to find the target nginx container:
1. Try docker-compose service label (most reliable)
2. Try container name with leading slash
3. Try container name without slash

This ensures compatibility across different docker-gen versions and container naming schemes.

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: groupsky

config/ingressgen/templates/nginx.tmpl

@@ -1,4 +1,10 @@
-{{ $TargetContainer := where $ "Name" (printf "/%s" $.Env.TARGET_CONTAINER) | first }}
+{{ $TargetContainer := whereLabelValueMatches $ "com.docker.compose.service" "ingress" | first }}
+{{ if not $TargetContainer }}
+{{ $TargetContainer = where $ "Name" (printf "/%s" $.Env.TARGET_CONTAINER) | first }}
+{{ end }}
+{{ if not $TargetContainer }}
+{{ $TargetContainer = where $ "Name" $.Env.TARGET_CONTAINER | first }}
+{{ end }}
 
 {{ $external_http_port := coalesce $.Env.HTTP_PORT "80" }}
 {{ $external_https_port := coalesce $.Env.HTTPS_PORT "443" }}