Diagnostics and reliability. Adds a dependency-free /healthz (and /install/ping) liveness route that returns only build/version with no database or auth, so a 1101 there cleanly indicates a Cloudflare platform/wedge issue rather than an app bug. Connection errors are now stripped of any secret-shaped text (UUIDs, passwords, tokens, proxy/subscription links) before being stored or logged, plus a rate-limited structured log line for easier diagnosis. Includes all 4.6.x fixes.