feat: initialize cart app with blueprints, templates, and CI

Extract cart, order, and orders blueprints with their service layer,
templates, Dockerfile (APP_MODULE=app:app, IMAGE=cart), entrypoint,
and Gitea CI workflow from the coop monolith.

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

app.py

@@ -0,0 +1,80 @@
+from __future__ import annotations
+
+from quart import g
+
+from shared.factory import create_base_app
+
+from suma_browser.app.bp import register_cart_bp, register_orders, register_cart_api
+from suma_browser.app.bp.cart.services import (
+    get_cart,
+    total,
+    get_calendar_cart_entries,
+    calendar_total,
+)
+
+
+async def _load_cart():
+    """Load the full cart for the cart app (before each request)."""
+    g.cart = await get_cart(g.s)
+
+
+async def cart_context() -> dict:
+    """
+    Cart app context processor.
+
+    - cart / calendar_cart_entries / total / calendar_total: direct DB
+      (cart app owns this data)
+    - cart_count: derived from cart + calendar entries (for _mini.html)
+    - menu_items: fetched from coop internal API
+    """
+    from shared.context import base_context
+    from shared.internal_api import get as api_get, dictobj
+
+    ctx = await base_context()
+
+    # Cart app owns cart data — use g.cart from _load_cart
+    cart = getattr(g, "cart", None) or []
+    cal_entries = await get_calendar_cart_entries(g.s)
+
+    ctx["cart"] = cart
+    ctx["calendar_cart_entries"] = cal_entries
+    ctx["total"] = total
+    ctx["calendar_total"] = calendar_total
+
+    # Also set cart_count so _mini.html works the same way
+    cart_qty = sum(ci.quantity for ci in cart) if cart else 0
+    ctx["cart_count"] = cart_qty + len(cal_entries)
+    ctx["cart_total"] = (total(cart) or 0) + (calendar_total(cal_entries) or 0)
+
+    # Menu items from coop API (wrapped for attribute access in templates)
+    menu_data = await api_get("coop", "/internal/menu-items")
+    ctx["menu_items"] = dictobj(menu_data) if menu_data else []
+
+    return ctx
+
+
+def create_app() -> "Quart":
+    app = create_base_app(
+        "cart",
+        context_fn=cart_context,
+        before_request_fns=[_load_cart],
+    )
+
+    # Cart blueprint at root (was /cart in monolith)
+    app.register_blueprint(
+        register_cart_bp(url_prefix="/"),
+        url_prefix="/",
+    )
+
+    # Orders blueprint
+    app.register_blueprint(
+        register_orders(url_prefix="/orders"),
+    )
+
+    # Internal API (server-to-server, CSRF-exempt)
+    app.register_blueprint(register_cart_api())
+
+    return app
+
+
+app = create_app()