Phase 0: Add _ctx_to_env() and render_to_sx_with_env() to shared/sx/helpers.py,
register_sx_layout() to shared/sx/layouts.py, and ~root-header/~root-mobile
wrapper defcomps to layout.sx. Convert built-in "root" layout to .sx.
Phases 1-3: Convert account (65→19 lines), federation (105→97 lines),
and orders (88→21 lines) to use register_sx_layout with .sx defcomps
that read ctx values as free variables from the evaluation environment.
No more Python building SX strings via SxExpr(await root_header_sx(ctx)).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>