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/sx/header.sx

@@ -24,3 +24,10 @@
   (div :id (str "entry-title-" entry-id) :class "flex gap-1 items-center"
     title times))
 
+(defcomp ~events-slot-label (&key name description)
+  (div :class "flex flex-col md:flex-row md:gap-2 items-center"
+    (div :class "flex flex-row items-center gap-2"
+      (i :class "fa fa-clock")
+      (div :class "shrink-0" name))
+    (p :class "text-stone-500 whitespace-pre-line break-all w-full" description)))
+