feat: add self-update command

Add 'kctl-tui update' subcommand that checks GitHub Releases for
new versions and replaces the running binary.

Uses github.com/creativeprojects/go-selfupdate for safe binary
replacement with automatic OS/arch detection.

Supports --verbose flag for detailed update progress logging.

cmd/kctl-tui/main.go

@@ -70,6 +70,12 @@ func main() {
 				os.Exit(1)
 			}
 			return
+		case "update":
+			if err := runUpdate(verbose); err != nil {
+				fmt.Fprintln(os.Stderr, "kctl-tui update error:", err)
+				os.Exit(1)
+			}
+			return
 		default:
 			fmt.Fprintf(os.Stderr, "unknown command: %s\n\n", filtered[0])
 			printUsage()
@@ -92,6 +98,7 @@ https://github.com/skoelle/kctl-tui
 Usage:
   kctl-tui [flags]             start the TUI (full navigation mode)
   kctl-tui doctor              check tools, config and connections
+  kctl-tui update              update to the latest release
   kctl-tui config check        validate ~/.kctl-tui/config.yaml
   kctl-tui panel [options]     control pane (called internally by tmux)
 
@@ -103,6 +110,7 @@ Flags:
 Examples:
   kctl-tui                          # start the TUI
   kctl-tui doctor                   # verify everything is installed
+  kctl-tui update                   # update to the latest version
   kctl-tui --verbose 2>debug.log    # log commands to a file
   kctl-tui config check             # validate config
 `)

cmd/kctl-tui/update.go

@@ -0,0 +1,72 @@
+// Copyright (c) 2026 Stefan Koelle (https://stefankoelle.de)
+// Licensed under the MIT License. See LICENSE file in project root for details.
+
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/creativeprojects/go-selfupdate"
+)
+
+const githubSlug = "skoelle/kctl-tui"
+
+func runUpdate(verbose bool) error {
+	if verbose {
+		selfupdate.SetLogger(&verboseLogger{})
+	}
+
+	current := version
+	if current == "dev" {
+		fmt.Fprintln(os.Stderr, "WARNING: running dev build — cannot compare versions")
+		fmt.Println("Skipping version check. Build from a tagged release to enable self-update.")
+		return nil
+	}
+
+	fmt.Printf("Current version: %s\n", current)
+	fmt.Println("Checking for updates...")
+
+	source, err := selfupdate.NewGitHubSource(selfupdate.GitHubConfig{})
+	if err != nil {
+		return fmt.Errorf("failed to init GitHub source: %w", err)
+	}
+
+	updater, err := selfupdate.NewUpdater(selfupdate.Config{
+		Source: source,
+	})
+	if err != nil {
+		return fmt.Errorf("failed to create updater: %w", err)
+	}
+
+	repo := selfupdate.ParseSlug(githubSlug)
+
+	rel, err := updater.UpdateSelf(context.Background(), current, repo)
+	if err != nil {
+		return fmt.Errorf("update failed: %w", err)
+	}
+
+	if rel != nil && rel.Version() != current {
+		fmt.Printf("Updated from %s to %s\n", current, rel.Version())
+	} else {
+		fmt.Println("Already up-to-date.")
+	}
+
+	return nil
+}
+
+type verboseLogger struct{}
+
+func (l *verboseLogger) Print(v ...any) {
+	fmt.Fprint(os.Stderr, v...)
+}
+
+func (l *verboseLogger) Printf(format string, v ...any) {
+	fmt.Fprintf(os.Stderr, format, v...)
+}
+
+func init() {
+	log.SetOutput(os.Stderr)
+}