Reject empty / whitespace / explicit-null / over-cap names with 400
instead of NREing on null assignment or storing arbitrarily-long
strings the DB column has no cap on. 24-char limit is a conservative
backstop against direct API abuse; the client UI enforces its own
keyboard limit.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Implements POST /account/update_name — writes Viewer.DisplayName and
returns an empty array per the prod capture. Includes TDD test covering
the persist side-effect.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>