Refactor aggregate alias validation in configuration. Updated the Validate function in config.go to improve error handling for unknown server aliases, ensuring clearer validation feedback for configuration entries.

internal/config/config.go

@@ -108,7 +108,7 @@ func (c *Config) Validate() error {
 			if a == "" {
 				return fmt.Errorf("aggregate.include_aliases[%d]: empty entry", i)
 			}
-			if !seen[a] {
+			if _, ok := seen[a]; !ok {
 				return fmt.Errorf("aggregate.include_aliases[%d]: unknown server alias %q", i, a)
 			}
 		}