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>

shared/sx/templates/auth.sx

@@ -30,6 +30,27 @@
     :link-label "account" :icon "fa-solid fa-user"
     :child-id "auth-header-child" :oob oob))
 
+;; Auto-fetching auth header — uses IO primitives, no free variables needed.
+;; Expands inline (defmacro) so IO calls resolve in _aser mode.
+(defmacro ~auth-header-row-auto (oob)
+  (quasiquote
+    (~auth-header-row :account-url (app-url "account" "")
+                       :select-colours (select-colours)
+                       :account-nav (account-nav-ctx)
+                       :oob (unquote oob))))
+
+(defmacro ~auth-header-row-simple-auto (oob)
+  (quasiquote
+    (~auth-header-row-simple :account-url (app-url "account" "")
+                              :oob (unquote oob))))
+
+;; Auto-fetching auth nav items — for mobile menus
+(defmacro ~auth-nav-items-auto ()
+  (quasiquote
+    (~auth-nav-items :account-url (app-url "account" "")
+                      :select-colours (select-colours)
+                      :account-nav (account-nav-ctx))))
+
 ;; Orders header row
 (defcomp ~orders-header-row (&key list-url)
   (~menu-row-sx :id "orders-row" :level 2 :colour "sky"