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>

events/bp/calendars/services/calendars.py

@@ -4,7 +4,8 @@ from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from models.calendars import Calendar
-from shared.services.registry import services
+from shared.infrastructure.data_client import fetch_data
+from shared.contracts.dtos import PostDTO, dto_from_dict
 from shared.services.relationships import attach_child, detach_child
 import unicodedata
 import re
@@ -49,7 +50,8 @@ def slugify(value: str, max_len: int = 255) -> str:
 
 
 async def soft_delete(sess: AsyncSession, post_slug: str, calendar_slug: str) -> bool:
-    post = await services.blog.get_post_by_slug(sess, post_slug)
+    raw = await fetch_data("blog", "post-by-slug", params={"slug": post_slug}, required=False)
+    post = dto_from_dict(PostDTO, raw) if raw else None
     if not post:
         return False
 
@@ -84,7 +86,8 @@ async def create_calendar(sess: AsyncSession, post_id: int, name: str) -> Calend
     slug=slugify(name)
 
     # Ensure post exists (avoid silent FK errors in some DBs)
-    post = await services.blog.get_post_by_id(sess, post_id)
+    raw = await fetch_data("blog", "post-by-id", params={"id": post_id}, required=False)
+    post = dto_from_dict(PostDTO, raw) if raw else None
     if not post:
         raise CalendarError(f"Post {post_id} does not exist.")