fix: resolve 5 bugs identified in code review

- Fix malformed YAML in config_test.go (incorrect indentation)
- Add validation for empty file_extensions in Config.Validate()
- Remove obsolete max_depth test case (field no longer exists)
- Remove unused global cfg variable in main.go
- Fix race condition in ScrapeSites by counting URLs before goroutines
- Remove unreachable JavaScript code in scroll script, add proper delay
- Standardize file extensions to not include leading dot

main.go

@@ -10,8 +10,6 @@ import (
 	"github.com/tnypxl/rollup/internal/scraper"
 )
 
-var cfg *config.Config
-
 func main() {
 	// Check if the command is "help"
 	isHelpCommand := len(os.Args) > 1 && (os.Args[1] == "help" || os.Args[1] == "--help" || os.Args[1] == "-h")