Add bind-ssh-tailscale.sh as standalone manual-run script

Places the script in standalone/ so it is excluded from setup.sh automation.
Documents manual curl-and-run usage in README.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

standalone/bind-ssh-tailscale.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+log() { echo "[$(date +'%Y-%m-%d %H:%M:%S')] $1"; }
+
+if [ "$EUID" -ne 0 ]; then
+    log "ERROR: Please run as root"
+    exit 1
+fi
+
+# Check Tailscale is installed and connected
+if ! command -v tailscale &>/dev/null; then
+    log "ERROR: Tailscale is not installed"
+    exit 1
+fi
+
+TAILSCALE_IP=$(tailscale ip -4 2>/dev/null)
+if [ -z "$TAILSCALE_IP" ]; then
+    log "ERROR: Could not get Tailscale IP — is Tailscale connected?"
+    exit 1
+fi
+log "Tailscale IP: ${TAILSCALE_IP}"
+
+# Detect SSH service name
+if systemctl is-active --quiet ssh 2>/dev/null; then
+    SSH_SERVICE="ssh"
+elif systemctl is-active --quiet sshd 2>/dev/null; then
+    SSH_SERVICE="sshd"
+else
+    log "ERROR: No running SSH service found (tried ssh, sshd)"
+    exit 1
+fi
+
+# Use a drop-in file if sshd_config.d exists, otherwise edit sshd_config directly
+if [ -d /etc/ssh/sshd_config.d ]; then
+    DROPIN="/etc/ssh/sshd_config.d/99-tailscale-only.conf"
+    [ -f "$DROPIN" ] && log "WARNING: ${DROPIN} already exists — overwriting"
+    cat > "$DROPIN" << EOF
+# Bind SSH to Tailscale interface only
+# To revert: rm ${DROPIN} && systemctl restart ${SSH_SERVICE}
+ListenAddress ${TAILSCALE_IP}
+PasswordAuthentication no
+PermitEmptyPasswords no
+EOF
+    log "Written: ${DROPIN}"
+else
+    BACKUP="/etc/ssh/sshd_config.bak.$(date +%Y%m%d_%H%M%S)"
+    cp /etc/ssh/sshd_config "$BACKUP"
+    log "Backed up sshd_config to ${BACKUP}"
+
+    # Remove any existing ListenAddress lines and add ours
+    sed -i '/^[#]*ListenAddress/d' /etc/ssh/sshd_config
+    echo "ListenAddress ${TAILSCALE_IP}" >> /etc/ssh/sshd_config
+    log "Updated /etc/ssh/sshd_config"
+fi
+
+# Validate config before restarting
+if ! sshd -t; then
+    log "ERROR: SSH config validation failed — aborting without restart"
+    [ -n "${DROPIN:-}" ] && rm -f "$DROPIN"
+    exit 1
+fi
+log "SSH config validated OK"
+
+systemctl restart "$SSH_SERVICE"
+log "SSH service restarted"
+
+log ""
+log "Done. SSH is now bound to Tailscale only (${TAILSCALE_IP})"
+log "Connect with: ssh root@${TAILSCALE_IP}"
+if [ -d /etc/ssh/sshd_config.d ]; then
+    log "To revert:    rm ${DROPIN} && systemctl restart ${SSH_SERVICE}"
+else
+    log "To revert:    cp ${BACKUP} /etc/ssh/sshd_config && systemctl restart ${SSH_SERVICE}"
+fi