Add interactive script to generate root .env for docker-compose

Prompts for DB password, public host, EMIT_SECRET, and SMTP creds,
auto-generating secrets where left blank, instead of hand-editing
.env.example.

docker/init-env.sh

@@ -0,0 +1,64 @@
+#!/bin/bash
+# Interactively creates the root .env file used by docker-compose.yml.
+# Run from the repo root: ./docker/init-env.sh
+set -e
+
+cd "$(dirname "$0")/.."
+ENV_FILE=".env"
+
+if [ -f "$ENV_FILE" ]; then
+	read -r -p "$ENV_FILE already exists — overwrite? [y/N] " confirm
+	case "$confirm" in
+		[yY]*) ;;
+		*) echo "Aborted."; exit 0 ;;
+	esac
+fi
+
+detected_ip=$(curl -s --max-time 3 ifconfig.me || true)
+
+echo
+echo "== Database =="
+read -r -s -p "DB root password [leave blank to auto-generate]: " db_pass; echo
+if [ -z "$db_pass" ]; then
+	db_pass=$(openssl rand -base64 24 | tr -d '/+=' | cut -c1-24)
+	echo "  generated: $db_pass"
+fi
+
+echo
+echo "== Server =="
+read -r -p "Public IP or domain the browser uses to reach this server [${detected_ip:-required}]: " public_host
+public_host=${public_host:-$detected_ip}
+if [ -z "$public_host" ]; then
+	echo "PUBLIC_HOST is required." >&2
+	exit 1
+fi
+
+read -r -p "HTTP port to expose [80]: " http_port
+http_port=${http_port:-80}
+
+echo
+echo "== PHP <-> Node shared secret =="
+read -r -p "EMIT_SECRET [leave blank to auto-generate]: " emit_secret
+if [ -z "$emit_secret" ]; then
+	emit_secret=$(openssl rand -hex 32)
+	echo "  generated: $emit_secret"
+fi
+
+echo
+echo "== SMTP (outgoing mail) =="
+read -r -p "SMTP username (email address): " smtp_user
+read -r -s -p "SMTP password (Gmail app password): " smtp_pass; echo
+
+cat > "$ENV_FILE" <<EOF
+DB_ROOT_PASSWORD=$db_pass
+PUBLIC_HOST=$public_host
+EMIT_SECRET=$emit_secret
+SMTP_USERNAME=$smtp_user
+SMTP_PASSWORD=$smtp_pass
+HTTP_PORT=$http_port
+EOF
+chmod 600 "$ENV_FILE"
+
+echo
+echo "Wrote $ENV_FILE (permissions 600)."
+echo "Next: docker compose up -d --build"