Replace env free-variable threading with IO-primitive auto-fetch macros

Layout components now self-resolve context (cart-mini, auth-menu, nav-tree,
rights, URLs) via new IO primitives (root-header-ctx, select-colours,
account-nav-ctx, app-rights) and defmacro wrappers (~root-header-auto,
~auth-header-row-auto, ~root-mobile-auto). This eliminates _ctx_to_env(),
HELPER_CSS_CLASSES, and verbose :key threading across all 10 services.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

events/sxc/pages/entries.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 
 from markupsafe import escape
 
-from shared.sx.helpers import render_to_sx, render_to_sx_with_env, _ctx_to_env
+from shared.sx.helpers import render_to_sx, render_to_sx_with_env
 from shared.sx.parser import SxExpr
 
 from .utils import (