Integrate go-altcha to protect login, change password, lost password,
and reset password forms against automated submissions. Serves the
altcha widget JS from the embedded library, exposes a challenge
endpoint, validates responses server-side with replay prevention, and
updates the CSP to allow self-hosted scripts and WebAssembly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
