fix: Skip shared domains during server restore to avoid invalid slot warning

Shared domains (with _shares key) have no server slots to restore,
so they should be skipped early in the restore loop.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

haproxy_mcp/tools/configuration.py

@@ -37,6 +37,9 @@ def restore_servers_from_config() -> int:
     server_info_list: list[tuple[str, str]] = []  # For logging on failure
 
     for domain, slots in config.items():
+        if "_shares" in slots:
+            continue
+
         backend = get_domain_backend(domain)
         if not backend:
             continue