feat: playground static site with cursor webhook deploy

Scaffold nginx + deploy-hook stack for playground.schwenk.online,
Gitea cursor workflow, directory-based public/ content, and boka
bootstrap via git clone.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy-hook/entrypoint.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [ -z "${WEBHOOK_SECRET:-}" ]; then
+  echo "Error: WEBHOOK_SECRET is not set"
+  exit 1
+fi
+
+envsubst < /etc/webhook/hooks.json.template > /tmp/hooks.json
+
+exec webhook -hooks /tmp/hooks.json -verbose