Move market composition from Python to .sx defcomps (Phase 3)

Python sxc/pages/ functions no longer build nested sx_call chains or
reference leaf component names. Instead they extract data (URLs, prices,
CSRF, cart state) and call a single top-level composition defcomp with
pure data values. The .sx defcomps handle all component-to-component
wiring, iteration (map), and conditional rendering.

New .sx composition defcomps:
- headers.sx: ~market-header-from-data, ~market-desktop-nav-from-data,
  ~market-product-header-from-data, ~market-product-admin-header-from-data
- prices.sx: ~market-prices-header-from-data, ~market-card-price-from-data
- navigation.sx: ~market-mobile-nav-from-data
- cards.sx: ~market-product-cards-content, ~market-card-from-data,
  ~market-cards-content, ~market-landing-from-data
- detail.sx: ~market-product-detail-from-data, ~market-detail-gallery-from-data,
  ~market-detail-info-from-data
- meta.sx: ~market-product-meta-from-data
- filters.sx: ~market-desktop-filter-from-data, ~market-mobile-chips-from-data,
  ~market-mobile-filter-content-from-data, plus 6 sub-composition defcomps

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

market/sx/prices.sx

@@ -32,3 +32,36 @@
 
 (defcomp ~market-prices-row (&key inner)
   (div :class "flex flex-row items-center justify-between md:gap-2 md:px-2" inner))
+
+
+;; ---------------------------------------------------------------------------
+;; Composition: prices header + cart button from data
+;; ---------------------------------------------------------------------------
+
+(defcomp ~market-prices-header-from-data (&key cart-id cart-action csrf quantity cart-href
+                                               sp-val sp-str rp-val rp-str rrp-str)
+  (~market-prices-row :inner
+    (<>
+      (if quantity
+        (~market-cart-add-quantity :cart-id cart-id :action cart-action :csrf csrf
+          :minus-val (str (- quantity 1)) :plus-val (str (+ quantity 1))
+          :quantity (str quantity) :cart-href cart-href)
+        (~market-cart-add-empty :cart-id cart-id :action cart-action :csrf csrf))
+      (when sp-val
+        (<> (~market-header-price-special-label)
+            (~market-header-price-special :price sp-str)
+            (when rp-val (~market-header-price-strike :price rp-str))))
+      (when (and (not sp-val) rp-val)
+        (<> (~market-header-price-regular-label)
+            (~market-header-price-regular :price rp-str)))
+      (when rrp-str (~market-header-rrp :rrp rrp-str)))))
+
+;; Card price line from data (used in product cards)
+(defcomp ~market-card-price-from-data (&key sp-val sp-str rp-val rp-str)
+  (~market-price-line :inner
+    (<>
+      (when sp-val
+        (<> (~market-price-special :price sp-str)
+            (when rp-val (~market-price-regular-strike :price rp-str))))
+      (when (and (not sp-val) rp-val)
+        (~market-price-regular :price rp-str)))))