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/types.py

@@ -240,9 +240,47 @@ class PageDef:
         return f"<page:{self.name} path={self.path!r}>"
 
 
+# ---------------------------------------------------------------------------
+# QueryDef / ActionDef
+# ---------------------------------------------------------------------------
+
+@dataclass
+class QueryDef:
+    """A declarative data query defined in an .sx file.
+
+    Created by ``(defquery name (&key param...) "docstring" body)``.
+    The body is evaluated with async I/O primitives to produce JSON data.
+    """
+    name: str
+    params: list[str]       # keyword parameter names
+    doc: str                # docstring
+    body: Any               # unevaluated s-expression body
+    closure: dict[str, Any] = field(default_factory=dict)
+
+    def __repr__(self):
+        return f"<query:{self.name}({', '.join(self.params)})>"
+
+
+@dataclass
+class ActionDef:
+    """A declarative action defined in an .sx file.
+
+    Created by ``(defaction name (&key param...) "docstring" body)``.
+    The body is evaluated with async I/O primitives to produce JSON data.
+    """
+    name: str
+    params: list[str]       # keyword parameter names
+    doc: str                # docstring
+    body: Any               # unevaluated s-expression body
+    closure: dict[str, Any] = field(default_factory=dict)
+
+    def __repr__(self):
+        return f"<action:{self.name}({', '.join(self.params)})>"
+
+
 # ---------------------------------------------------------------------------
 # Type alias
 # ---------------------------------------------------------------------------
 
 # An s-expression value after evaluation
-SExp = int | float | str | bool | Symbol | Keyword | Lambda | Macro | Component | HandlerDef | RelationDef | PageDef | list | dict | _Nil | None
+SExp = int | float | str | bool | Symbol | Keyword | Lambda | Macro | Component | HandlerDef | RelationDef | PageDef | QueryDef | ActionDef | list | dict | _Nil | None