system updater: complete overhaul

Move system update flow to GO, with a CLI (convenient AIO tool) and
server integration. All lifecycle, scheduling, execution occurs on
backend side.

Run some backends via pkexec, some via terminal like paru/yay.

Incorporate flatpak as an option to update.

Add terminal override setting in GUI, in addition to $TERMINAL env
variable.

fixes #2307
fixes #822
fixes #1102
fixes #1812
fixes #1087
fixes #1743

core/internal/server/sysupdate/backend_zypper.go

@@ -0,0 +1,78 @@
+package sysupdate
+
+import (
+	"context"
+	"encoding/xml"
+	"errors"
+	"os/exec"
+)
+
+func init() {
+	RegisterSystemBackend(func() Backend { return &zypperBackend{} })
+}
+
+type zypperBackend struct{}
+
+func (zypperBackend) ID() string                         { return "zypper" }
+func (zypperBackend) DisplayName() string                { return "Zypper" }
+func (zypperBackend) Repo() RepoKind                     { return RepoSystem }
+func (zypperBackend) NeedsAuth() bool                    { return true }
+func (zypperBackend) RunsInTerminal() bool               { return false }
+func (zypperBackend) IsAvailable(_ context.Context) bool { return commandExists("zypper") }
+
+type zypperUpdateList struct {
+	XMLName xml.Name       `xml:"stream"`
+	Updates []zypperUpdate `xml:"update-list>update"`
+}
+
+type zypperUpdate struct {
+	Name       string `xml:"name,attr"`
+	Edition    string `xml:"edition,attr"`
+	EditionOld string `xml:"edition-old,attr"`
+	Kind       string `xml:"kind,attr"`
+}
+
+func (zypperBackend) CheckUpdates(ctx context.Context) ([]Package, error) {
+	cmd := exec.CommandContext(ctx, "zypper", "--non-interactive", "--xmlout", "list-updates")
+	out, err := cmd.Output()
+	if err != nil {
+		if exitErr, ok := errors.AsType[*exec.ExitError](err); ok {
+			switch exitErr.ExitCode() {
+			case 100, 101, 102, 103:
+				err = nil
+			}
+		}
+		if err != nil {
+			return nil, err
+		}
+	}
+	return parseZypperXML(out)
+}
+
+func parseZypperXML(out []byte) ([]Package, error) {
+	var list zypperUpdateList
+	if err := xml.Unmarshal(out, &list); err != nil {
+		return nil, err
+	}
+	pkgs := make([]Package, 0, len(list.Updates))
+	for _, u := range list.Updates {
+		if u.Kind != "" && u.Kind != "package" {
+			continue
+		}
+		pkgs = append(pkgs, Package{
+			Name:        u.Name,
+			Repo:        RepoSystem,
+			Backend:     "zypper",
+			FromVersion: u.EditionOld,
+			ToVersion:   u.Edition,
+		})
+	}
+	return pkgs, nil
+}
+
+func (zypperBackend) Upgrade(ctx context.Context, opts UpgradeOptions, onLine func(string)) error {
+	if opts.DryRun {
+		return Run(ctx, []string{"zypper", "--non-interactive", "--dry-run", "update"}, RunOptions{OnLine: onLine})
+	}
+	return Run(ctx, []string{"pkexec", "zypper", "--non-interactive", "update"}, RunOptions{OnLine: onLine})
+}