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>

shared/infrastructure/factory.py

@@ -117,6 +117,15 @@ def create_base_app(
     load_shared_components()
     load_relation_registry()
 
+    # Load defquery/defaction definitions from {service}/queries.sx and actions.sx
+    from shared.sx.query_registry import load_service_protocols
+    _app_root = Path(os.getcwd())
+    load_service_protocols(name, str(_app_root))
+
+    # Register /internal/schema endpoint for protocol introspection
+    from shared.infrastructure.schema_blueprint import create_schema_blueprint
+    app.register_blueprint(create_schema_blueprint(name))
+
     # Load CSS registry (tw.css → class-to-rule lookup for on-demand CSS)
     from shared.sx.css_registry import load_css_registry, registry_loaded
     _styles = BASE_DIR / "static" / "styles"