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/status.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 statusCmd = &cobra.Command{
@@ -37,6 +37,10 @@ func runStatus(cmd *cobra.Command, args []string) error {
 	}
 
 	prefix, suffix := cfg.Prefix, cfg.Suffix
+	ini, err := initsys.New(cfg)
+	if err != nil {
+		return err
+	}
 
 	if len(cfg.Units) == 0 {
 		fmt.Println("No units configured. Run 'unitdore syncup' to discover containers.")
@@ -65,13 +69,13 @@ func runStatus(cmd *cobra.Command, args []string) error {
 		}
 
 		installed := "yes"
-		if !systemd.IsInstalled(u, prefix, suffix) {
+		if !ini.IsInstalled(u, prefix, suffix) {
 			installed = "no"
 		}
 
 		state := "—"
-		if systemd.IsInstalled(u, prefix, suffix) {
-			state = systemd.Status(u, prefix, suffix)
+		if ini.IsInstalled(u, prefix, suffix) {
+			state = ini.Status(u, prefix, suffix)
 		}
 
 		rows = append(rows, statusRow{