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)

market/bp/cart/services/__init__.py

@@ -0,0 +1,2 @@
+from .total import total
+from .identity import CartIdentity, current_cart_identity

market/bp/cart/services/identity.py

@@ -0,0 +1,4 @@
+# Re-export from canonical shared location
+from shared.infrastructure.cart_identity import CartIdentity, current_cart_identity
+
+__all__ = ["CartIdentity", "current_cart_identity"]

market/bp/cart/services/total.py

@@ -0,0 +1,6 @@
+def total(cart):
+    return sum(
+        (item.product.special_price or item.product.regular_price) * item.quantity
+        for item in cart
+        if (item.product.special_price or item.product.regular_price) is not None
+    )