Replace inter-service _handlers dicts with declarative sx defquery/defaction

The inter-service data layer (fetch_data/call_action) was the least
structured part of the codebase — Python _handlers dicts with ad-hoc
param extraction scattered across 16 route files. This replaces them
with declarative .sx query/action definitions that make the entire
inter-service protocol self-describing and greppable.

Infrastructure:
- defquery/defaction special forms in the sx evaluator
- Query/action registry with load, lookup, and schema introspection
- Query executor using async_eval with I/O primitives
- Blueprint factories (create_data_blueprint/create_action_blueprint)
  with sx-first dispatch and Python fallback
- /internal/schema endpoint on every service
- parse-datetime and split-ids primitives for type coercion

Service extractions:
- LikesService (toggle, is_liked, liked_slugs, liked_ids)
- PageConfigService (ensure, get_by_container, get_by_id, get_batch, update)
- RelationsService (wraps module-level functions)
- AccountDataService (user_by_email, newsletters)
- CartItemsService, MarketDataService (raw SQLAlchemy lookups)

50 of 54 handlers converted to sx, 4 Python fallbacks remain
(ghost-sync/push-member, clear-cart-for-order, create-order).
Net: -1,383 lines Python, +251 lines modified.

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

cart/bp/data/routes.py

@@ -1,79 +1,14 @@
 """Cart app data endpoints.
 
-Exposes read-only JSON queries at ``/internal/data/<query_name>`` for
-cross-app callers via the internal data client.
+All queries are defined in ``cart/queries.sx``.
 """
 from __future__ import annotations
 
-from quart import Blueprint, g, jsonify, request
+from quart import Blueprint
 
-from shared.infrastructure.data_client import DATA_HEADER
-from shared.contracts.dtos import dto_to_dict
-from shared.services.registry import services
+from shared.infrastructure.query_blueprint import create_data_blueprint
 
 
 def register() -> Blueprint:
-    bp = Blueprint("data", __name__, url_prefix="/internal/data")
-
-    @bp.before_request
-    async def _require_data_header():
-        if not request.headers.get(DATA_HEADER):
-            return jsonify({"error": "forbidden"}), 403
-        from shared.infrastructure.internal_auth import validate_internal_request
-        if not validate_internal_request():
-            return jsonify({"error": "forbidden"}), 403
-
-    _handlers: dict[str, object] = {}
-
-    @bp.get("/<query_name>")
-    async def handle_query(query_name: str):
-        handler = _handlers.get(query_name)
-        if handler is None:
-            return jsonify({"error": "unknown query"}), 404
-        result = await handler()
-        return jsonify(result)
-
-    # --- cart-summary ---
-    async def _cart_summary():
-        user_id = request.args.get("user_id", type=int)
-        session_id = request.args.get("session_id")
-        page_slug = request.args.get("page_slug")
-        summary = await services.cart.cart_summary(
-            g.s, user_id=user_id, session_id=session_id, page_slug=page_slug,
-        )
-        return dto_to_dict(summary)
-
-    _handlers["cart-summary"] = _cart_summary
-
-    # --- cart-items (product slugs + quantities for template rendering) ---
-    async def _cart_items():
-        from sqlalchemy import select
-        from shared.models.market import CartItem
-
-        user_id = request.args.get("user_id", type=int)
-        session_id = request.args.get("session_id")
-
-        filters = [CartItem.deleted_at.is_(None)]
-        if user_id is not None:
-            filters.append(CartItem.user_id == user_id)
-        elif session_id is not None:
-            filters.append(CartItem.session_id == session_id)
-        else:
-            return []
-
-        result = await g.s.execute(
-            select(CartItem).where(*filters)
-        )
-        items = result.scalars().all()
-        return [
-            {
-                "product_id": item.product_id,
-                "product_slug": item.product_slug,
-                "quantity": item.quantity,
-            }
-            for item in items
-        ]
-
-    _handlers["cart-items"] = _cart_items
-
+    bp, _handlers = create_data_blueprint("cart")
     return bp