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/evaluator.py

@@ -553,6 +553,75 @@ def _sf_defhandler(expr: list, env: dict) -> HandlerDef:
     return handler
 
 
+def _parse_key_params(params_expr: list) -> list[str]:
+    """Parse ``(&key param1 param2 ...)`` into a list of param name strings."""
+    params: list[str] = []
+    in_key = False
+    for p in params_expr:
+        if isinstance(p, Symbol):
+            if p.name == "&key":
+                in_key = True
+                continue
+            if in_key:
+                params.append(p.name)
+        elif isinstance(p, str):
+            params.append(p)
+    return params
+
+
+def _sf_defquery(expr: list, env: dict):
+    """``(defquery name (&key param...) "docstring" body)``"""
+    from .types import QueryDef
+    if len(expr) < 4:
+        raise EvalError("defquery requires name, params, and body")
+    name_sym = expr[1]
+    if not isinstance(name_sym, Symbol):
+        raise EvalError(f"defquery name must be symbol, got {type(name_sym).__name__}")
+    params_expr = expr[2]
+    if not isinstance(params_expr, list):
+        raise EvalError("defquery params must be a list")
+    params = _parse_key_params(params_expr)
+    # Optional docstring before body
+    if len(expr) >= 5 and isinstance(expr[3], str):
+        doc = expr[3]
+        body = expr[4]
+    else:
+        doc = ""
+        body = expr[3]
+    qdef = QueryDef(
+        name=name_sym.name, params=params, doc=doc,
+        body=body, closure=dict(env),
+    )
+    env[f"query:{name_sym.name}"] = qdef
+    return qdef
+
+
+def _sf_defaction(expr: list, env: dict):
+    """``(defaction name (&key param...) "docstring" body)``"""
+    from .types import ActionDef
+    if len(expr) < 4:
+        raise EvalError("defaction requires name, params, and body")
+    name_sym = expr[1]
+    if not isinstance(name_sym, Symbol):
+        raise EvalError(f"defaction name must be symbol, got {type(name_sym).__name__}")
+    params_expr = expr[2]
+    if not isinstance(params_expr, list):
+        raise EvalError("defaction params must be a list")
+    params = _parse_key_params(params_expr)
+    if len(expr) >= 5 and isinstance(expr[3], str):
+        doc = expr[3]
+        body = expr[4]
+    else:
+        doc = ""
+        body = expr[3]
+    adef = ActionDef(
+        name=name_sym.name, params=params, doc=doc,
+        body=body, closure=dict(env),
+    )
+    env[f"action:{name_sym.name}"] = adef
+    return adef
+
+
 def _sf_set_bang(expr: list, env: dict) -> Any:
     """``(set! name value)`` — mutate existing binding."""
     if len(expr) != 3:
@@ -737,6 +806,8 @@ _SPECIAL_FORMS: dict[str, Any] = {
     "quasiquote": _sf_quasiquote,
     "defhandler": _sf_defhandler,
     "defpage": _sf_defpage,
+    "defquery": _sf_defquery,
+    "defaction": _sf_defaction,
 }