Adds a /terms page and links it from the site footer and from the
"I agree to the Terms and Conditions" checkbox on registration, which
previously didn't point anywhere.
Registration now requires agreeing to the Terms and Conditions and lets
users opt in to hear about future projects. The opt-in is persisted on
the user via a new marketing_opt_in column (migration included).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Frank