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/assets/assets.go

@@ -0,0 +1,72 @@
+// Package assets hält die eingebetteten Presets und Custom-Scripte.
+package assets
+
+import (
+	"embed"
+	"strings"
+)
+
+//go:embed presets scripts
+var embedded embed.FS
+
+// ScriptContent liefert den Inhalt einer gebündelten Script-Vorlage.
+func ScriptContent(name string) (string, bool) {
+	b, err := embedded.ReadFile("scripts/" + name)
+	if err != nil {
+		return "", false
+	}
+	return string(b), true
+}
+
+// ScriptNames listet alle gebündelten Script-Vorlagen.
+func ScriptNames() []string {
+	entries, err := embedded.ReadDir("scripts")
+	if err != nil {
+		return nil
+	}
+	names := make([]string, 0, len(entries))
+	for _, e := range entries {
+		if !e.IsDir() {
+			names = append(names, e.Name())
+		}
+	}
+	return names
+}
+
+// PresetFiles liefert Dateiname → Inhalt aller eingebetteten Presets.
+func PresetFiles() map[string]string {
+	entries, err := embedded.ReadDir("presets")
+	if err != nil {
+		return nil
+	}
+	files := make(map[string]string, len(entries))
+	for _, e := range entries {
+		if e.IsDir() {
+			continue
+		}
+		if b, err := embedded.ReadFile("presets/" + e.Name()); err == nil {
+			files[e.Name()] = string(b)
+		}
+	}
+	return files
+}
+
+// MatchScript findet die Vorlage, deren Inhalt zu content passt, und
+// erkennt damit bereits installierte motd-assist-Scripte.
+func MatchScript(content string) (string, bool) {
+	return MatchScriptBytes([]byte(content))
+}
+
+// MatchScriptBytes ist die Byte-Variante von MatchScript.
+func MatchScriptBytes(b []byte) (string, bool) {
+	content := strings.TrimSpace(string(b))
+	if content == "" {
+		return "", false
+	}
+	for _, name := range ScriptNames() {
+		if c, ok := ScriptContent(name); ok && strings.TrimSpace(c) == content {
+			return name, true
+		}
+	}
+	return "", false
+}