feat: add motd-assist TUI for managing dynamic MOTDs

Initial Go project built with Bubble Tea and Lip Gloss:
- Live preview and management of /etc/update-motd.d scripts
- Embedded presets (ubuntu-default, minimal, server-dashboard)
- Bundled POSIX sh style scripts (brand header, sysinfo panel, footer)
- Snapshot/restore safety around applying changes
- CLI subcommands preview, apply, restore, list-presets
- Unit tests for detect, sanitize, and apply logic

internal/motd/detect.go

@@ -0,0 +1,74 @@
+package motd
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// HostInfo beschreibt den erkannten MOTD-Zustand des Systems.
+type HostInfo struct {
+	Hostname    string
+	Distro      string   // PRETTY_NAME aus /etc/os-release
+	PAM         bool     // pam_motd konfiguriert (dynamischer MOTD aktiv)
+	PAMWhere    []string // Dateien in /etc/pam.d mit pam_motd-Eintrag
+	DynamicPath string   // vorhandene Cache-Datei der dynamischen MOTD ("" = keine)
+	StaticMOTD  bool     // /etc/motd vorhanden und nicht leer
+}
+
+// DetectHost sammelt Host- und MOTD-Informationen unter root.
+// Fehler einzelner Erkennungen führen nicht zum Abbruch.
+func DetectHost(root string) HostInfo {
+	info := HostInfo{Hostname: "unbekannt", Distro: "unbekannt"}
+
+	if h, err := os.Hostname(); err == nil && h != "" {
+		info.Hostname = strings.SplitN(h, ".", 2)[0]
+	}
+	if pretty, ok := osReleaseValue(filepath.Join(root, "etc", "os-release"), "PRETTY_NAME"); ok {
+		info.Distro = pretty
+	}
+
+	for _, svc := range []string{"sshd", "login", "remote"} {
+		b, err := os.ReadFile(filepath.Join(root, "etc", "pam.d", svc))
+		if err != nil {
+			continue
+		}
+		for _, line := range strings.Split(string(b), "\n") {
+			line = strings.TrimSpace(line)
+			if line == "" || strings.HasPrefix(line, "#") {
+				continue
+			}
+			if strings.Contains(line, "pam_motd") {
+				info.PAM = true
+				info.PAMWhere = append(info.PAMWhere, svc)
+				break
+			}
+		}
+	}
+
+	for _, cand := range []string{"run/motd.dynamic", "run/motd"} {
+		p := filepath.Join(root, cand)
+		if fi, err := os.Stat(p); err == nil && !fi.IsDir() && fi.Size() > 0 {
+			info.DynamicPath = p
+			break
+		}
+	}
+
+	if fi, err := os.Stat(filepath.Join(root, "etc", "motd")); err == nil && !fi.IsDir() && fi.Size() > 0 {
+		info.StaticMOTD = true
+	}
+	return info
+}
+
+func osReleaseValue(path, key string) (string, bool) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return "", false
+	}
+	for _, line := range strings.Split(string(b), "\n") {
+		if v, ok := strings.CutPrefix(strings.TrimSpace(line), key+"="); ok {
+			return strings.Trim(v, `"'`), true
+		}
+	}
+	return "", false
+}