Add macros, declarative handlers (defhandler), and convert all fragment routes to sx

Phase 1 — Macros: defmacro + quasiquote syntax (`, ,, ,@) in parser,
evaluator, HTML renderer, and JS mirror. Macro type, expansion, and
round-trip serialization.

Phase 2 — Expanded primitives: app-url, url-for, asset-url, config,
format-date, parse-int (pure); service, request-arg, request-path,
nav-tree, get-children (I/O); jinja-global, relations-from (pure).
Updated _io_service to accept (service "registry-name" "method" :kwargs)
with auto kebab→snake conversion. DTO-to-dict now expands datetime fields
into year/month/day convenience keys. Tuple returns converted to lists.

Phase 3 — Declarative handlers: HandlerDef type, defhandler special form,
handler registry (service → name → HandlerDef), async evaluator+renderer
(async_eval.py) that awaits I/O primitives inline within control flow.
Handler loading from .sx files, execute_handler, blueprint factory.

Phase 4 — Convert all fragment routes: 13 Python fragment handlers across
8 services replaced with declarative .sx handler files. All routes.py
simplified to uniform sx dispatch pattern. Two Jinja HTML handlers
(events/container-cards, events/account-page) kept as Python.

New files: shared/sx/async_eval.py, shared/sx/handlers.py,
shared/sx/tests/test_handlers.py, plus 13 handler .sx files under
{service}/sx/handlers/. MarketService.product_by_slug() added.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/types.py

@@ -127,6 +127,29 @@ class Lambda:
         return evaluator(self.body, local)
 
 
+# ---------------------------------------------------------------------------
+# Macro
+# ---------------------------------------------------------------------------
+
+@dataclass
+class Macro:
+    """A macro — an AST-transforming function.
+
+    Created by ``(defmacro name (params... &rest rest) body)``.
+    Receives unevaluated arguments, evaluates its body to produce a new
+    s-expression, which is then evaluated in the caller's environment.
+    """
+    params: list[str]
+    rest_param: str | None    # &rest parameter name
+    body: Any                 # unevaluated — returns an s-expression to eval
+    closure: dict[str, Any] = field(default_factory=dict)
+    name: str | None = None
+
+    def __repr__(self):
+        tag = self.name or "macro"
+        return f"<{tag}({', '.join(self.params)})>"
+
+
 # ---------------------------------------------------------------------------
 # Component
 # ---------------------------------------------------------------------------
@@ -149,6 +172,27 @@ class Component:
         return f"<Component ~{self.name}({', '.join(self.params)})>"
 
 
+# ---------------------------------------------------------------------------
+# HandlerDef
+# ---------------------------------------------------------------------------
+
+@dataclass
+class HandlerDef:
+    """A declarative fragment handler defined in an .sx file.
+
+    Created by ``(defhandler name (&key param...) body)``.
+    The body is evaluated in a sandboxed environment with only
+    s-expression primitives available.
+    """
+    name: str
+    params: list[str]       # keyword parameter names
+    body: Any               # unevaluated s-expression body
+    closure: dict[str, Any] = field(default_factory=dict)
+
+    def __repr__(self):
+        return f"<handler:{self.name}({', '.join(self.params)})>"
+
+
 # ---------------------------------------------------------------------------
 # RelationDef
 # ---------------------------------------------------------------------------
@@ -174,4 +218,4 @@ class RelationDef:
 # ---------------------------------------------------------------------------
 
 # An s-expression value after evaluation
-SExp = int | float | str | bool | Symbol | Keyword | Lambda | Component | RelationDef | list | dict | _Nil | None
+SExp = int | float | str | bool | Symbol | Keyword | Lambda | Macro | Component | HandlerDef | RelationDef | list | dict | _Nil | None