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/browser.sx

@@ -169,3 +169,43 @@
 (define now-ms
   (fn ()
     (host-call (host-global "Date") "now")))
+
+
+;; --------------------------------------------------------------------------
+;; Scheduling
+;; --------------------------------------------------------------------------
+
+(define schedule-idle
+  (fn (f)
+    (let ((cb (host-callback f)))
+      (if (host-get (dom-window) "requestIdleCallback")
+        (host-call (dom-window) "requestIdleCallback" cb)
+        (set-timeout cb 0)))))
+
+
+;; --------------------------------------------------------------------------
+;; Cookies
+;; --------------------------------------------------------------------------
+
+(define set-cookie
+  (fn (name value days)
+    (let ((d (or days 365))
+          (expires (host-call
+                     (host-new "Date"
+                       (+ (host-call (host-global "Date") "now")
+                          (* d 864e5)))
+                     "toUTCString")))
+      (host-set! (dom-document) "cookie"
+        (str name "="
+             (host-call nil "encodeURIComponent" value)
+             ";expires=" expires ";path=/;SameSite=Lax")))))
+
+(define get-cookie
+  (fn (name)
+    (let ((cookies (host-get (dom-document) "cookie"))
+          (match (host-call cookies "match"
+                   (host-new "RegExp"
+                     (str "(?:^|;\\s*)" name "=([^;]*)")))))
+      (if match
+        (host-call nil "decodeURIComponent" (host-get match 1))
+        nil))))