refactor: replace empty slice literal with var declaration

This PR streamlines slice declarations by replacing an empty slice literal with a var declaration. The change removes unnecessary allocation and embraces Go’s idiomatic use of nil slices for empty collections.

- Empty slice literal used to declare a variable: The code originally declared an empty slice with [][]string{}, which allocates a zero-length slice. By switching to `var extras [][]string`, we declare a nil slice that behaves identically in append scenarios but avoids an extra allocation and better communicates intent.

> This Autofix was generated by AI. Please review the change before merging.

Author: deepsource-autofix[bot]

internal/ui.go

@@ -37,7 +37,7 @@ func displaySignalResult(result *tmhi.SignalResult) {
 	}
 
 	if result.FiveG != nil {
-		extras := [][]string{}
+		var extras [][]string
 		if result.FiveG.AntennaUsed != "" {
 			extras = append(extras, []string{"Antenna", result.FiveG.AntennaUsed})
 		}