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/scripts/brand-header

@@ -0,0 +1,36 @@
+#!/bin/sh
+# motd-assist :: brand-header — Rahmen-Header mit Hostname und Betriebssystem
+set -u
+
+E=$(printf '\033')
+BLUE="${E}[1;38;5;75m"
+ORANGE="${E}[1;38;5;214m"
+DIM="${E}[2m"
+BOLD="${E}[1m"
+R="${E}[0m"
+
+HOST=$(hostname 2>/dev/null || echo localhost)
+HOST=${HOST%%.*}
+
+OS=Linux
+if [ -r /etc/os-release ]; then
+	. /etc/os-release
+	OS=${PRETTY_NAME:-Linux}
+fi
+
+W=${COLUMNS:-72}
+case $W in ''|*[!0-9]*) W=72 ;; esac
+[ "$W" -gt 78 ] && W=78
+[ "$W" -lt 44 ] && W=44
+
+INNER=$((W - 2))
+PLAIN=" ${HOST} - ${OS} "
+PAD=$((INNER - ${#PLAIN}))
+[ "$PAD" -lt 0 ] && PAD=0
+
+RULE=$(awk -v n="$INNER" 'BEGIN{s="";for(i=0;i<n;i++)s=s "─";printf "%s",s}')
+SPACES=$(printf '%*s' "$PAD" '')
+
+printf '%b\n' "$BLUE╭$R$DIM$RULE$R$BLUE╮$R"
+printf '%b\n' "$BLUE│$R $BOLD$BLUE$HOST$R $DIM·$R $ORANGE$OS$R$SPACES $BLUE│$R"
+printf '%b\n' "$BLUE╰$R$DIM$RULE$R$BLUE╯$R"

internal/assets/scripts/footer

@@ -0,0 +1,14 @@
+#!/bin/sh
+# motd-assist :: footer — dezente Kernel-/Uptime-Zeile
+set -u
+
+E=$(printf '\033')
+DIM="${E}[2m"
+R="${E}[0m"
+
+K=$(uname -r 2>/dev/null || echo unknown)
+UP=$(uptime -p 2>/dev/null)
+[ -n "$UP" ] || UP=$(awk '{d=int($1/86400); h=int(($1%86400)/3600); printf "up %d days %d hours", d, h}' /proc/uptime 2>/dev/null)
+
+[ -n "$UP" ] && printf '%b\n' "${DIM}${K} · ${UP}${R}"
+exit 0

internal/assets/scripts/sysinfo-panel

@@ -0,0 +1,66 @@
+#!/bin/sh
+# motd-assist :: sysinfo-panel — Load, Speicher, Disk und Updates als farbige Balken
+set -u
+
+E=$(printf '\033')
+GREEN="${E}[38;5;114m"
+YELLOW="${E}[38;5;221m"
+RED="${E}[38;5;203m"
+LBLUE="${E}[38;5;75m"
+DIM="${E}[2m"
+R="${E}[0m"
+
+BAR=22
+
+# bar <used> <total> — farbiger Balken mit Prozentanzeige
+bar() {
+	awk -v u="$1" -v t="$2" -v b="$BAR" -v g="$GREEN" -v y="$YELLOW" -v r="$RED" -v d="$DIM" -v rset="$R" 'BEGIN{
+		if (t <= 0) { printf "%sn/a%s", d, rset; exit }
+		pct = u * 100 / t
+		if (pct > 100) pct = 100
+		f = int(pct / 100 * b + 0.5)
+		c = (pct < 60) ? g : ((pct < 85) ? y : r)
+		s = c
+		for (i = 0; i < f; i++) s = s "━"
+		s = s d
+		for (i = f; i < b; i++) s = s "·"
+		printf "%s%s%s %s%3d%%%s", s, rset, c, c, pct, rset
+	}'
+}
+
+mem=$(awk '/^MemTotal:/ {t=$2} /^MemAvailable:/ {a=$2} END {if (t>0) printf "%.0f %.0f", t-a, t}' /proc/meminfo 2>/dev/null)
+[ -n "$mem" ] && printf '%b\n' "$LBLUE MEM  $DIM│$R $(bar $mem)"
+
+disk=$(df -P / 2>/dev/null | awk 'NR==2 {gsub("%","",$5); print $5}')
+[ -n "$disk" ] && printf '%b\n' "$LBLUE DISK $DIM│$R $(bar $disk 100)"
+
+if [ -r /proc/loadavg ]; then
+	load=$(awk '{print $1}' /proc/loadavg)
+	ncpu=$(getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1)
+	case $ncpu in ''|*[!0-9]*) ncpu=1 ;; esac
+	awk -v l="$load" -v n="$ncpu" -v b="$BAR" -v g="$GREEN" -v y="$YELLOW" -v r="$RED" -v d="$DIM" -v rset="$R" -v lbl="$LBLUE" 'BEGIN{
+		pct = l * 100 / n
+		if (pct > 100) pct = 100
+		f = int(pct / 100 * b + 0.5)
+		c = (pct < 60) ? g : ((pct < 85) ? y : r)
+		s = c
+		for (i = 0; i < f; i++) s = s "━"
+		s = s d
+		for (i = f; i < b; i++) s = s "·"
+		printf "%s LOAD %s│%s %s%s%s %s%s/%s%s\n", lbl, d, rset, s, rset, c, c, l, n, rset
+	}'
+fi
+
+if [ -r /var/lib/update-notifier/updates-available ]; then
+	upd=$(awk 'NR==1 {print $1; exit}' /var/lib/update-notifier/updates-available 2>/dev/null)
+	case $upd in
+		''|*[!0-9]*) ;;
+		*)
+			awk -v n="$upd" -v g="$GREEN" -v y="$YELLOW" -v r="$RED" -v d="$DIM" -v rset="$R" -v lbl="$LBLUE" 'BEGIN{
+				c = (n == 0) ? g : ((n < 20) ? y : r)
+				txt = (n == 0) ? "System ist auf dem aktuellen Stand" : n " Paket-Updates verfügbar"
+				printf "%s UPD  %s│%s %s%s%s\n", lbl, d, rset, c, txt, rset
+			}'
+			;;
+	esac
+fi