infra: add setup_server.sh for one-time server provisioning

Creates the beanflows system user, /opt/beanflows directory, and an
ed25519 GitLab deploy key. Prints the public key to add as a read-only
deploy key on the repo.

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

infra/setup_server.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+# One-time server setup: create app user, /opt/beanflows, and GitLab deploy key.
+# Run as root on a fresh Hetzner server before bootstrapping the supervisor.
+#
+# Usage:
+#   bash infra/setup_server.sh
+
+set -euo pipefail
+
+APP_USER="beanflows"
+APP_DIR="/opt/beanflows"
+KEY_PATH="/home/$APP_USER/.ssh/gitlab_deploy"
+
+# Create system user with a home dir (needed for .ssh) but no login shell
+if ! id "$APP_USER" &>/dev/null; then
+    useradd --system --create-home --shell /usr/sbin/nologin "$APP_USER"
+    echo "Created user: $APP_USER"
+else
+    echo "User $APP_USER already exists, skipping"
+fi
+
+# Create app directory owned by app user
+mkdir -p "$APP_DIR"
+chown "$APP_USER:$APP_USER" "$APP_DIR"
+chmod 750 "$APP_DIR"
+echo "Created $APP_DIR (owner: $APP_USER)"
+
+# Generate deploy key if not already present
+if [ ! -f "$KEY_PATH" ]; then
+    mkdir -p "/home/$APP_USER/.ssh"
+    ssh-keygen -t ed25519 -f "$KEY_PATH" -N "" -C "beanflows-server"
+    chown -R "$APP_USER:$APP_USER" "/home/$APP_USER/.ssh"
+    chmod 700 "/home/$APP_USER/.ssh"
+    chmod 600 "$KEY_PATH"
+    chmod 644 "$KEY_PATH.pub"
+    echo "Generated deploy key: $KEY_PATH"
+else
+    echo "Deploy key already exists, skipping"
+fi
+
+echo ""
+echo "=== Add this deploy key to GitLab ==="
+echo "GitLab → repo → Settings → Repository → Deploy Keys (read-only)"
+echo ""
+cat "$KEY_PATH.pub"