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/stopall.go

@@ -6,7 +6,7 @@ import (
 
 	"github.com/spf13/cobra"
 	"github.com/warkanum/unitdore/config"
-	"github.com/warkanum/unitdore/systemd"
+	"github.com/warkanum/unitdore/initsys"
 )
 
 var stopallCmd = &cobra.Command{
@@ -27,6 +27,10 @@ func runStopall(cmd *cobra.Command, args []string) error {
 	}
 
 	prefix, suffix := cfg.Prefix, cfg.Suffix
+	ini, err := initsys.New(cfg)
+	if err != nil {
+		return err
+	}
 
 	// Reverse order for shutdown
 	units := make([]config.Unit, len(cfg.Units))
@@ -42,11 +46,11 @@ func runStopall(cmd *cobra.Command, args []string) error {
 	failed := 0
 
 	for _, u := range units {
-		if !systemd.IsInstalled(u, prefix, suffix) {
+		if !ini.IsInstalled(u, prefix, suffix) {
 			continue
 		}
-		fmt.Printf("  ■ stopping: %s...\n", systemd.ServiceName(u, prefix, suffix))
-		if err := systemd.Stop(u, prefix, suffix); err != nil {
+		fmt.Printf("  ■ stopping: %s...\n", ini.ServiceName(u, prefix, suffix))
+		if err := ini.Stop(u, prefix, suffix); err != nil {
 			fmt.Printf("  ✗ failed: %s: %v\n", u.Name, err)
 			failed++
 		} else {