Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

cart/bp/cart/services/calendar_cart.py

@@ -0,0 +1,45 @@
+from __future__ import annotations
+
+from decimal import Decimal
+
+from shared.services.registry import services
+from .identity import current_cart_identity
+
+
+async def get_calendar_cart_entries(session):
+    """
+    Return all *pending* calendar entries (as CalendarEntryDTOs) for the
+    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"],
+    )
+
+
+def calendar_total(entries) -> Decimal:
+    """
+    Total cost of pending calendar entries.
+    """
+    return sum(
+        (Decimal(str(e.cost)) if e.cost else Decimal(0))
+        for e in entries
+        if e.cost is not None
+    )
+
+
+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"],
+    )
+
+
+def ticket_total(tickets) -> Decimal:
+    """Total cost of reserved tickets."""
+    return sum((Decimal(str(t.price)) if t.price else Decimal(0) for t in tickets), Decimal(0))