Move SX construction from Python to .sx defcomps (phases 0-4)

Eliminate Python s-expression string building across account, orders,
federation, and cart services. Visual rendering logic now lives entirely
in .sx defcomp components; Python files contain only data serialization,
header/layout wiring, and thin wrappers that call defcomps.

Phase 0: Shared DRY extraction — auth/orders header defcomps, format-decimal/
pluralize/escape/route-prefix primitives.
Phase 1: Account — dashboard, newsletters, login/device/check-email content.
Phase 2: Orders — order list, detail, filter, checkout return assembled defcomps.
Phase 3: Federation — social nav, post cards, timeline, search, actors,
notifications, compose, profile assembled defcomps.
Phase 4: Cart — overview, page cart items/calendar/tickets/summary, admin,
payments assembled defcomps; orders rendering reuses Phase 2 shared defcomps.

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

cart/sx/overview.sx

@@ -39,3 +39,56 @@
 (defcomp ~cart-overview-panel (&key cards)
   (div :class "max-w-full px-3 py-3 space-y-3"
     (div :class "space-y-4" cards)))
+
+(defcomp ~cart-empty ()
+  (div :class "max-w-full px-3 py-3 space-y-3"
+    (div :class "rounded-2xl border border-dashed border-stone-300 bg-white/80 p-6 sm:p-8 text-center"
+      (~empty-state :icon "fa fa-shopping-cart" :message "Your cart is empty" :cls "text-center"))))
+
+;; Assembled page group card — replaces Python _page_group_card_sx
+(defcomp ~cart-page-group-card-from-data (&key grp cart-url-base)
+  (let* ((post (get grp "post"))
+         (product-count (or (get grp "product_count") 0))
+         (calendar-count (or (get grp "calendar_count") 0))
+         (ticket-count (or (get grp "ticket_count") 0))
+         (total (or (get grp "total") 0))
+         (market-place (get grp "market_place"))
+         (badges (<>
+           (when (> product-count 0)
+             (~cart-badge :icon "fa fa-box-open"
+               :text (str product-count " item" (pluralize product-count))))
+           (when (> calendar-count 0)
+             (~cart-badge :icon "fa fa-calendar"
+               :text (str calendar-count " booking" (pluralize calendar-count))))
+           (when (> ticket-count 0)
+             (~cart-badge :icon "fa fa-ticket"
+               :text (str ticket-count " ticket" (pluralize ticket-count)))))))
+    (if post
+      (let* ((slug (or (get post "slug") ""))
+             (title (or (get post "title") ""))
+             (feature-image (get post "feature_image"))
+             (mp-name (if market-place (or (get market-place "name") "") ""))
+             (display-title (if (!= mp-name "") mp-name title)))
+        (~cart-group-card
+          :href (str cart-url-base "/" slug "/")
+          :img (if feature-image
+                 (~cart-group-card-img :src feature-image :alt title)
+                 (~img-or-placeholder :src nil :size-cls "h-16 w-16 rounded-xl"
+                   :placeholder-icon "fa fa-store text-xl"))
+          :display-title display-title
+          :subtitle (when (!= mp-name "")
+            (~cart-mp-subtitle :title title))
+          :badges (~cart-badges-wrap :badges badges)
+          :total (str "\u00a3" (format-decimal total 2))))
+      (~cart-orphan-card
+        :badges (~cart-badges-wrap :badges badges)
+        :total (str "\u00a3" (format-decimal total 2))))))
+
+;; Assembled cart overview content — replaces Python _overview_main_panel_sx
+(defcomp ~cart-overview-content (&key page-groups cart-url-base)
+  (if (empty? page-groups)
+    (~cart-empty)
+    (~cart-overview-panel
+      :cards (map (lambda (grp)
+        (~cart-page-group-card-from-data :grp grp :cart-url-base cart-url-base))
+        page-groups))))