Step 5p6 lazy loading + Step 6b VM transpilation prep

Lazy module loading (Step 5 piece 6 completion):
- Add define-library wrappers + import declarations to 13 source .sx files
- compile-modules.js generates module-manifest.json with dependency graph
- compile-modules.js strips define-library/import before bytecode compilation
  (VM doesn't handle these as special forms)
- sx-platform.js replaces hardcoded 24-file loadWebStack() with manifest-driven
  recursive loader — only downloads modules the page needs
- Result: 12 modules loaded (was 24), zero errors, zero warnings
- Fallback to full load if manifest missing

VM transpilation prep (Step 6b):
- Refactor lib/vm.sx: 20 accessor functions replace raw dict access
- Factor out collect-n-from-stack, collect-n-pairs, pad-n-nils helpers
- bootstrap_vm.py: transpiles 9 VM logic functions to OCaml
- sx_vm_ref.ml: proof that vm.sx transpiles (preamble has stubs)

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

web/lib/browser.sx

@@ -1,3 +1,7 @@
+(define-library (sx browser)
+  (export browser-location-href browser-location-pathname browser-location-origin browser-same-origin? url-pathname browser-push-state browser-replace-state browser-reload browser-navigate local-storage-get local-storage-set local-storage-remove set-timeout set-interval clear-timeout clear-interval request-animation-frame fetch-request new-abort-controller controller-signal controller-abort promise-then promise-resolve promise-delayed browser-confirm browser-prompt browser-media-matches? json-parse log-info log-warn console-log now-ms schedule-idle set-cookie get-cookie)
+  (begin
+
 (define
   browser-location-href
   (fn () (host-get (host-get (dom-window) "location") "href")))
@@ -219,3 +223,9 @@
             "match"
             (host-new "RegExp" (str "(?:^|;\\s*)" name "=([^;]*)")))))
       (if match (host-call nil "decodeURIComponent" (host-get match 1)) nil))))
+
+
+))
+
+;; Re-export to global env
+(import (sx browser))