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>

cart/bp/cart/services/calendar_cart.py

@@ -2,7 +2,8 @@ from __future__ import annotations
 
 from decimal import Decimal
 
-from shared.services.registry import services
+from shared.infrastructure.data_client import fetch_data
+from shared.contracts.dtos import CalendarEntryDTO, TicketDTO, dto_from_dict
 from .identity import current_cart_identity
 
 
@@ -12,11 +13,13 @@ async def get_calendar_cart_entries(session):
     current cart identity (user or anonymous session).
     """
     ident = current_cart_identity()
-    return await services.calendar.pending_entries(
-        session,
-        user_id=ident["user_id"],
-        session_id=ident["session_id"],
-    )
+    params = {}
+    if ident["user_id"] is not None:
+        params["user_id"] = ident["user_id"]
+    if ident["session_id"] is not None:
+        params["session_id"] = ident["session_id"]
+    raw = await fetch_data("events", "pending-entries", params=params, required=False) or []
+    return [dto_from_dict(CalendarEntryDTO, e) for e in raw]
 
 
 def calendar_total(entries) -> Decimal:
@@ -33,11 +36,13 @@ def calendar_total(entries) -> Decimal:
 async def get_ticket_cart_entries(session):
     """Return all reserved tickets (as TicketDTOs) for the current identity."""
     ident = current_cart_identity()
-    return await services.calendar.pending_tickets(
-        session,
-        user_id=ident["user_id"],
-        session_id=ident["session_id"],
-    )
+    params = {}
+    if ident["user_id"] is not None:
+        params["user_id"] = ident["user_id"]
+    if ident["session_id"] is not None:
+        params["session_id"] = ident["session_id"]
+    raw = await fetch_data("events", "pending-tickets", params=params, required=False) or []
+    return [dto_from_dict(TicketDTO, t) for t in raw]
 
 
 def ticket_total(tickets) -> Decimal: