feat: OpenRC and runit init backends behind an Init interface

Extract init-neutral unit resolution into service/, add initsys.Init with systemd, openrc and runit backends, selected by 'init:' config or autodetect. OpenRC and runit are root only; rootless units run as system services as that user. Add docs and generated examples for all three.

cmd/list.go

@@ -7,7 +7,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/warkanum/unitdore/config"
-	"github.com/warkanum/unitdore/systemd"
+	"github.com/warkanum/unitdore/initsys"
 )
 
 var listCmd = &cobra.Command{
@@ -41,6 +41,10 @@ func runList(cmd *cobra.Command, args []string) error {
 	})
 
 	prefix, suffix := cfg.Prefix, cfg.Suffix
+	ini, err := initsys.New(cfg)
+	if err != nil {
+		return err
+	}
 
 	type row struct{ name, runtime, enabled, installed, path string }
 
@@ -53,9 +57,9 @@ func runList(cmd *cobra.Command, args []string) error {
 
 		installed := "no"
 		unitPath := "—"
-		if p, err := systemd.UnitPath(u, prefix, suffix); err == nil {
+		if p, err := ini.UnitPath(u, prefix, suffix); err == nil {
 			unitPath = p
-			if systemd.IsInstalled(u, prefix, suffix) {
+			if ini.IsInstalled(u, prefix, suffix) {
 				installed = "yes"
 			}
 		}