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/html.py

@@ -27,8 +27,8 @@ from __future__ import annotations
 import contextvars
 from typing import Any
 
-from .types import Component, Keyword, Lambda, NIL, Symbol
-from .evaluator import _eval, _call_component
+from .types import Component, Keyword, Lambda, Macro, NIL, Symbol
+from .evaluator import _eval, _call_component, _expand_macro
 
 # ContextVar for collecting CSS class names during render.
 # Set to a set[str] to collect; None to skip.
@@ -360,6 +360,8 @@ _RENDER_FORMS: dict[str, Any] = {
     "map-indexed": _rsf_map_indexed,
     "filter": _rsf_filter,
     "for-each": _rsf_for_each,
+    "defmacro": _rsf_define,   # side-effect only, returns ""
+    "defhandler": _rsf_define, # side-effect only, returns ""
 }
 
 
@@ -420,6 +422,13 @@ def _render_list(expr: list, env: dict[str, Any]) -> str:
         if name in _RENDER_FORMS:
             return _RENDER_FORMS[name](expr, env)
 
+        # --- Macro expansion → expand then render --------------------------
+        if name in env:
+            val = env[name]
+            if isinstance(val, Macro):
+                expanded = _expand_macro(val, expr[1:], env)
+                return _render(expanded, env)
+
         # --- HTML tag → render as element ---------------------------------
         if name in HTML_TAGS:
             return _render_element(name, expr[1:], env)