Version 0.52.0

Added a page and a machine-readable file saying where to report a security problem.

The channel already existed — the question form has taken reports without an account since 10 August, and hands back a reference number and a reading code so you can read the answer. What was missing was the sign: a researcher arriving cold found no /.well-known/security.txt, no robots.txt and no sitemap, on a service that had been public for two weeks. All three are now live, the footer carries a Security reports link on every screen a visitor sees, and the new page says what is in scope, what to write, and what NMTS can and cannot see. There is no reward programme.

Fixed the title of the FAQ and security pages being covered by the top bar on narrow screens.