Decouple all cross-app service calls to HTTP endpoints

Replace every direct cross-app services.* call with HTTP-based
communication: call_action() for writes, fetch_data() for reads.
Each app now registers only its own domain service.

Infrastructure:
- shared/infrastructure/actions.py — POST client for /internal/actions/
- shared/infrastructure/data_client.py — GET client for /internal/data/
- shared/contracts/dtos.py — dto_to_dict/dto_from_dict serialization

Action endpoints (writes):
- events: 8 handlers (ticket adjust, claim/confirm, toggle, adopt)
- market: 2 handlers (create/soft-delete marketplace)
- cart: 1 handler (adopt cart for user)

Data endpoints (reads):
- blog: 4 (post-by-slug/id, posts-by-ids, search-posts)
- events: 10 (pending entries/tickets, entries/tickets for page/order,
  entry-ids, associated-entries, calendars, visible-entries-for-period)
- market: 1 (marketplaces-for-container)
- cart: 1 (cart-summary)

Service registration cleanup:
- blog→blog+federation, events→calendar+federation,
  market→market+federation, cart→cart only,
  federation→federation only, account→nothing
- Stubs reduced to minimal StubFederationService

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

blog/bp/post/routes.py

@@ -12,7 +12,8 @@ from quart import (
 )
 from .services.post_data import post_data
 from .services.post_operations import toggle_post_like
-from shared.services.registry import services
+from shared.infrastructure.data_client import fetch_data
+from shared.contracts.dtos import CartSummaryDTO, dto_from_dict
 from shared.infrastructure.fragments import fetch_fragment, fetch_fragments
 
 from shared.browser.app.redis_cacher import cache_page, clear_cache
@@ -92,14 +93,17 @@ def register():
               "container_nav_html": container_nav_html,
           }
 
-          # Page cart badge via service
+          # Page cart badge via HTTP
           post_dict = p_data.get("post") or {}
           if post_dict.get("is_page"):
               ident = current_cart_identity()
-              page_summary = await services.cart.cart_summary(
-                  g.s, user_id=ident["user_id"], session_id=ident["session_id"],
-                  page_slug=post_dict["slug"],
-              )
+              summary_params = {"page_slug": post_dict["slug"]}
+              if ident["user_id"] is not None:
+                  summary_params["user_id"] = ident["user_id"]
+              if ident["session_id"] is not None:
+                  summary_params["session_id"] = ident["session_id"]
+              raw_summary = await fetch_data("cart", "cart-summary", params=summary_params, required=False)
+              page_summary = dto_from_dict(CartSummaryDTO, raw_summary) if raw_summary else CartSummaryDTO()
               ctx["page_cart_count"] = page_summary.count + page_summary.calendar_count + page_summary.ticket_count
               ctx["page_cart_total"] = float(page_summary.total + page_summary.calendar_total + page_summary.ticket_total)