Paths

• / — request path through Cloudflare, NLB and nginx
• /postback — partner postback page, shows query parameters
• /api/postback — JSON, any method (GET/POST)
• /api/echo — request details as JSON
• /headers — request details as plain text
• /healthz — 200 ok
• /status/400 · 403 · 404 · 429 · 500 · 503 — fixed error codes, for testing Cloudflare and nginx error handling