feat(packages): implement PlanForce to reinstall all packages

Adds Reinstall method to PackageManager and AURHelper interfaces
so modules can invoke the concrete Reinstall helpers behind the
interface. *Pacman and *Yay already satisfy it.

internal/platform/pkgmgr.go

@@ -8,6 +8,7 @@ type PackageManager interface {
 	Name() string
 	IsInstalled(ctx context.Context, pkg string) (bool, error)
 	Install(ctx context.Context, pkgs []string) error
+	Reinstall(ctx context.Context, pkgs []string) error
 	Update(ctx context.Context) error
 }