Replace direct MarketPlace imports with MarketService calls

Market CRUD in blog now delegates to services.market.create_marketplace()
and soft_delete_marketplace() instead of importing MarketPlace directly.
Adds TODO comments on Calendar imports in admin routes (deferred to
admin UI rework). Updates shared submodule.

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

bp/post/admin/routes.py

@@ -191,7 +191,7 @@ def register():
   @require_admin
   async def calendar_view(slug: str, calendar_id: int):
     """Show calendar month view for browsing entries"""
-    from shared.models.calendars import Calendar
+    from shared.models.calendars import Calendar  # TODO: service method when admin UI is reworked
     from sqlalchemy import select
     from datetime import datetime, timezone
     from quart import request
@@ -273,7 +273,7 @@ def register():
   @require_admin
   async def entries(slug: str):
     from ..services.entry_associations import get_post_entry_ids
-    from shared.models.calendars import Calendar
+    from shared.models.calendars import Calendar  # TODO: service method when admin UI is reworked
     from sqlalchemy import select
 
     post_id = g.post_data["post"]["id"]
@@ -309,7 +309,7 @@ def register():
   @require_admin
   async def toggle_entry(slug: str, entry_id: int):
     from ..services.entry_associations import toggle_entry_association, get_post_entry_ids, get_associated_entries
-    from shared.models.calendars import Calendar
+    from shared.models.calendars import Calendar  # TODO: service method when admin UI is reworked
     from sqlalchemy import select
     from quart import jsonify