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

scripts/e2e-wsl.sh

@@ -0,0 +1,50 @@
+#!/bin/bash
+# End-to-End-Test für motd-assist in einem Fake-Root.
+set -euo pipefail
+cd /mnt/c/Users/janik.dietz/Coding/motd-assist
+go build -o /tmp/motd-assist .
+
+R=/tmp/motdroot
+rm -rf "$R"
+mkdir -p "$R/etc/update-motd.d" "$R/etc/pam.d"
+printf 'NAME="Ubuntu"\nPRETTY_NAME="Ubuntu 24.04.1 LTS"\n' > "$R/etc/os-release"
+printf 'session optional pam_motd.so motd=/run/motd.dynamic\n' > "$R/etc/pam.d/sshd"
+printf '#!/bin/sh\necho Welcome to Ubuntu \\e[1m %s\\e[0m\n' "$(hostname)" > "$R/etc/update-motd.d/00-header"
+printf '#!/bin/sh\necho " * Documentation: man handbook"\n' > "$R/etc/update-motd.d/10-help-text"
+chmod 755 "$R/etc/update-motd.d/00-header"
+chmod 644 "$R/etc/update-motd.d/10-help-text"
+
+echo "=== list (vorher) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist list
+
+echo
+echo "=== preview (vorher, nur 00-header aktiv) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist preview -w 60
+
+echo
+echo "=== apply server-dashboard (als root) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist apply server-dashboard
+
+echo
+echo "=== list (nachher) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist list
+
+echo
+echo "=== preview (nachher, Breite 60) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist preview -w 60
+
+echo
+echo "=== preview (nachher, Breite 40 — schmaler) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist preview -w 40 | cat -v | head -6
+
+echo
+echo "=== restore ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist restore
+
+echo
+echo "=== list (nach restore) ==="
+MOTD_ASSIST_ROOT=$R /tmp/motd-assist list
+
+echo
+echo "=== ls update-motd.d ==="
+ls -la "$R/etc/update-motd.d"