perf: increase parallel install workers from 1 to 4

Increases maxWorkers from 1 to 4 for parallel CLI package installation.
This aligns with the project convention (max 4 workers for brew) and
significantly speeds up installation when multiple packages are queued.

Casks remain sequential due to potential password prompts for .pkg installers.

Author: Jerry Xie

internal/brew/brew.go

@@ -16,7 +16,7 @@ import (
 	"github.com/openbootdotdev/openboot/internal/ui"
 )
 
-const maxWorkers = 1
+const maxWorkers = 4
 
 type OutdatedPackage struct {
 	Name    string