feat: order/delay in service files, enable cmd, --all on unit commands

- install/uninstall/start/stop/enable take <name> or --all; *all kept as shortcuts
- add enable (enable at boot + start); startall no longer enables
- order/delay resolved by config.ResolveOrder and written into systemd,
  OpenRC and runit service files (After=/sleep), so they apply at boot
- install --all stops and disables units before removing their files
- update regenerates all installed, enabled units and removes disabled ones
- edit creates the config dir; docs and man page updated
- tests: fake Init for cmd, ResolveOrder, backend ordering output

cmd/helpers.go

@@ -1,7 +1,10 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
+	"github.com/spf13/cobra"
+	"io"
 
 	"github.com/warkanum/unitdore/config"
 	"github.com/warkanum/unitdore/initsys"
@@ -17,10 +20,51 @@ func runtimeLabel(u config.Unit) string {
 }
 
 // lingerHint prints, once per user, how to make user units start at boot.
-func lingerHint(ini initsys.Init, seen map[string]bool, u config.Unit) {
+func lingerHint(w io.Writer, ini initsys.Init, seen map[string]bool, u config.Unit) {
 	if !ini.SupportsLinger() || u.User == "" || seen[u.User] || sysuser.LingerEnabled(u.User) {
 		return
 	}
 	seen[u.User] = true
-	fmt.Printf("  ! linger not enabled for %s — user units won't start at boot: sudo loginctl enable-linger %s\n", u.User, u.User)
+	fmt.Fprintf(w, "  ! linger not enabled for %s — user units won't start at boot: sudo loginctl enable-linger %s\n", u.User, u.User)
+}
+
+// nameOrAll requires exactly one unit name, or none when --all is set.
+func nameOrAll(all *bool) cobra.PositionalArgs {
+	return func(cmd *cobra.Command, args []string) error {
+		if *all {
+			if len(args) != 0 {
+				return errors.New("--all takes no unit name")
+			}
+			return nil
+		}
+		if len(args) != 1 {
+			return errors.New("requires a unit name, or --all")
+		}
+		return nil
+	}
+}
+
+// installedUnit finds a unit by name and checks that its service file exists.
+func installedUnit(cfg *config.Config, ini initsys.Init, name string) (*config.Unit, error) {
+	u := cfg.FindUnit(name)
+	if u == nil {
+		return nil, fmt.Errorf("unit %q not found", name)
+	}
+	if !ini.IsInstalled(*u, cfg.Prefix, cfg.Suffix) {
+		return nil, fmt.Errorf("%s is not installed — run 'unitdore install %s' first", name, name)
+	}
+	return u, nil
+}
+
+// loadInit loads the config and selects the init backend.
+func loadInit() (*config.Config, initsys.Init, error) {
+	cfg, err := config.Load(configPath)
+	if err != nil {
+		return nil, nil, err
+	}
+	ini, err := initsys.New(cfg)
+	if err != nil {
+		return nil, nil, err
+	}
+	return cfg, ini, nil
 }