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/harness-web.sx

@@ -1,3 +1,7 @@
+(define-library (sx harness-web)
+  (export mock-element mock-set-text! mock-append-child! mock-set-attr! mock-get-attr mock-add-listener! simulate-click simulate-input simulate-event assert-text assert-attr assert-class assert-no-class assert-child-count assert-event-fired assert-no-event event-fire-count make-web-harness is-renderable? is-render-leak? assert-renderable render-body-audit assert-render-body-clean mock-render mock-render-fragment assert-single-render-root assert-tag)
+  (begin
+
 (define
   mock-element
   :effects ()
@@ -318,3 +322,9 @@
     (assert
       (= (get el "tag") expected-tag)
       (str "Expected <" expected-tag "> but got <" (get el "tag") ">"))))
+
+
+))
+
+;; Re-export to global env
+(import (sx harness-web))