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>

market/queries.sx

@@ -0,0 +1,14 @@
+;; Market service — inter-service data queries
+
+(defquery marketplaces-for-container (&key type id)
+  "Marketplaces attached to a container (page, etc)."
+  (service "market" "marketplaces-for-container"
+    :container-type type :container-id id))
+
+(defquery products-by-ids (&key ids)
+  "Return product details for comma-separated IDs."
+  (service "market-data" "products-by-ids" :ids (split-ids ids)))
+
+(defquery marketplaces-by-ids (&key ids)
+  "Return marketplace data for comma-separated IDs."
+  (service "market-data" "marketplaces-by-ids" :ids (split-ids ids)))