feat(arch/binary): convert .pkg.tar.zst to Zeta binary package

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <[email protected]>

internal/arch/binary/frontend.go

@@ -3,8 +3,6 @@
 package binary
 
 import (
-	"errors"
-
 	"git.spectoria.dev/huntedbytheirs/zeta-reconstruct/internal/registry"
 )
 
@@ -13,9 +11,10 @@ type frontend struct{}
 
 func (frontend) Name() string { return "arch-binary" }
 
+// Convert converts an Arch .pkg.tar.zst into a Zeta binary package
+// (payload tarball + archive-mode package.lua) under opts.Output.
 func (frontend) Convert(input string, opts registry.Options) error {
-	// Implemented in a later todo (.pkg.tar.zst -> tarball + package.lua).
-	return errors.New("not implemented")
+	return Convert(input, opts)
 }
 
 func init() {