Fix examples.sx: paren balance + dict eval crash at startup

1. Extra closing paren in ex-tabs handler
2. tab-content dict values contained (div ...) HTML tags which crash
   during register_components since HTML primitives aren't in env

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

shared/sx/ref/boundary.sx

@@ -202,6 +202,13 @@
   :doc "All form fields as a dict."
   :context :request)
 
+(define-io-primitive "request-form-list"
+  :params (field-name)
+  :returns "list"
+  :async true
+  :doc "All values for a multi-value form field as a list."
+  :context :request)
+
 (define-io-primitive "request-headers-all"
   :params ()
   :returns "dict"