Adds /admin.html — a passphrase-gated, in-site admin console for diagnostics
and testing: API connectivity check, DB snapshot, browser smoke test, and
demo-data seed/clean. Gate is SHA-256 obfuscation only (default passphrase
"prime-admin"); restrict at the network/proxy for real protection.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
