feat: show page cart badge in blog post header (Phase 4)

Fetches page-scoped cart count from /internal/cart/summary?page_slug=
for page posts and displays a cart icon with count in the post header
that links to the page cart.

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

bp/post/routes.py

@@ -65,6 +65,7 @@ def register():
       p_data = getattr(g, "post_data", None)
       if p_data:
           from .services.entry_associations import get_associated_entries
+          from shared.internal_api import get as api_get
 
           db_post_id = (g.post_data.get("post") or {}).get("id")  # <-- integer
           calendars = (
@@ -86,13 +87,30 @@ def register():
           # Fetch associated entries for nav display
           associated_entries = await get_associated_entries(g.s, db_post_id)
 
-          return {
+          ctx = {
               **p_data,
               "base_title": f"{config()['title']} {p_data['post']['title']}",
               "calendars": calendars,
               "markets": markets,
               "associated_entries": associated_entries,
           }
+
+          # Page cart badge: fetch page-scoped cart count for pages
+          post_dict = p_data.get("post") or {}
+          if post_dict.get("is_page"):
+              page_cart = await api_get(
+                  "cart",
+                  f"/internal/cart/summary?page_slug={post_dict['slug']}",
+                  forward_session=True,
+              )
+              if page_cart:
+                  ctx["page_cart_count"] = page_cart.get("count", 0) + page_cart.get("calendar_count", 0)
+                  ctx["page_cart_total"] = page_cart.get("total", 0) + page_cart.get("calendar_total", 0)
+              else:
+                  ctx["page_cart_count"] = 0
+                  ctx["page_cart_total"] = 0
+
+          return ctx
       else:
         return {}