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/sx/query_executor.py

@@ -0,0 +1,70 @@
+"""
+Execute defquery / defaction definitions.
+
+Unlike fragment handlers (which produce SX markup via ``async_eval_to_sx``),
+query/action defs produce **data** (dicts, lists, scalars) that get
+JSON-serialized by the calling blueprint.  Uses ``async_eval()`` with
+the I/O primitive pipeline so ``(service ...)`` calls are awaited inline.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from .types import QueryDef, ActionDef, NIL
+
+
+async def execute_query(query_def: QueryDef, params: dict[str, str]) -> Any:
+    """Execute a defquery and return a JSON-serializable result.
+
+    Parameters are bound from request query string args.
+    """
+    from .jinja_bridge import get_component_env, _get_request_context
+    from .async_eval import async_eval
+
+    env = dict(get_component_env())
+    env.update(query_def.closure)
+
+    # Bind params from request args (try kebab-case and snake_case)
+    for param in query_def.params:
+        snake = param.replace("-", "_")
+        val = params.get(param, params.get(snake, NIL))
+        # Coerce type=int for common patterns
+        if isinstance(val, str) and val.lstrip("-").isdigit():
+            val = int(val)
+        env[param] = val
+
+    ctx = _get_request_context()
+    result = await async_eval(query_def.body, env, ctx)
+    return _normalize(result)
+
+
+async def execute_action(action_def: ActionDef, payload: dict[str, Any]) -> Any:
+    """Execute a defaction and return a JSON-serializable result.
+
+    Parameters are bound from the JSON request body.
+    """
+    from .jinja_bridge import get_component_env, _get_request_context
+    from .async_eval import async_eval
+
+    env = dict(get_component_env())
+    env.update(action_def.closure)
+
+    # Bind params from JSON payload (try kebab-case and snake_case)
+    for param in action_def.params:
+        snake = param.replace("-", "_")
+        val = payload.get(param, payload.get(snake, NIL))
+        env[param] = val
+
+    ctx = _get_request_context()
+    result = await async_eval(action_def.body, env, ctx)
+    return _normalize(result)
+
+
+def _normalize(value: Any) -> Any:
+    """Ensure result is JSON-serializable (strip NIL, convert sets, etc)."""
+    if value is NIL or value is None:
+        return None
+    if isinstance(value, set):
+        return list(value)
+    return value