Platform FFI reduction: remove 99 redundant PRIMITIVES registrations

Move DOM/browser operations to SX library wrappers (dom.sx, browser.sx)
using the 8 FFI primitives, eliminating duplicate native implementations.
Add scope-emitted transpiler rename — fixes 199 pre-existing test failures.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web/lib/dom.sx

@@ -263,6 +263,29 @@
 (define event-detail
   (fn (evt) (host-get evt "detail")))
 
+(define prevent-default
+  (fn (e) (when e (host-call e "preventDefault"))))
+
+(define stop-propagation
+  (fn (e) (when e (host-call e "stopPropagation"))))
+
+(define event-modifier-key?
+  (fn (e)
+    (and e (or (host-get e "ctrlKey") (host-get e "metaKey")
+               (host-get e "shiftKey") (host-get e "altKey")))))
+
+(define element-value
+  (fn (el)
+    (if (and el (not (nil? (host-get el "value"))))
+      (host-get el "value")
+      nil)))
+
+(define error-message
+  (fn (e)
+    (if (and e (host-get e "message"))
+      (host-get e "message")
+      (str e))))
+
 
 ;; --------------------------------------------------------------------------
 ;; DOM data storage