Extend defhandler with :path/:method/:csrf, migrate 12 ref endpoints to SX

defhandler now supports keyword options for public route registration:
  (defhandler name :path "/..." :method :post :csrf false (&key) body)

Infrastructure: forms.sx parses options, HandlerDef stores path/method/csrf,
register_route_handlers() mounts path-based handlers as app routes.

New IO primitives (boundary.sx "Web interop" section): now, sleep,
request-form, request-json, request-header, request-content-type.

First migration: 12 reference API endpoints from Python f-string SX
to declarative .sx handlers in sx/sx/handlers/ref-api.sx.

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

shared/sx/ref/platform_py.py

@@ -222,8 +222,14 @@ def make_macro(params, rest_param, body, env, name=None):
                  closure=dict(env), name=name)
 
 
-def make_handler_def(name, params, body, env):
-    return HandlerDef(name=name, params=list(params), body=body, closure=dict(env))
+def make_handler_def(name, params, body, env, opts=None):
+    path = opts.get('path') if opts else None
+    method = str(opts.get('method', 'get')) if opts else 'get'
+    csrf = opts.get('csrf', True) if opts else True
+    if isinstance(csrf, str):
+        csrf = csrf.lower() not in ('false', 'nil', 'no')
+    return HandlerDef(name=name, params=list(params), body=body, closure=dict(env),
+                      path=path, method=method.lower(), csrf=csrf)
 
 
 def make_query_def(name, params, doc, body, env):