VM import suspension for browser lazy loading

Bytecode compiler now emits OP_PERFORM for (import ...) and compiles
(define-library ...) bodies. The VM stores the import request in
globals["__io_request"] and stops the run loop — no exceptions needed.
vm-execute-module returns a suspension dict, vm-resume-module continues.

Browser: sx_browser.ml detects suspension dicts from execute_module and
returns JS {suspended, op, request, resume} objects. The sx-platform.js
while loop handles cascading suspensions via handleImportSuspension.

13 modules load via .sxbc bytecode in 226ms (manifest-driven), both
islands hydrate, all handlers wired. 2650/2650 tests pass including
6 new vm-import-suspension tests.

Also: consolidated sx-platform-2.js → sx-platform.js, fixed
vm-execute-module missing code-from-value call, fixed bootstrap.py
protocol registry transpiler issues.

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

hosts/ocaml/browser/build-all.sh

@@ -26,7 +26,7 @@ cp dist/sx_browser.bc.wasm.js "$DEST/"
 cp dist/sx_browser.bc.js "$DEST/"
 rm -rf "$DEST/sx_browser.bc.wasm.assets"
 cp -r dist/sx_browser.bc.wasm.assets "$DEST/"
-cp dist/sx-platform.js "$DEST/sx-platform-2.js"
+cp dist/sx-platform.js "$DEST/sx-platform.js"
 cp dist/sx/*.sx "$DEST/sx/"
 cp dist/sx/*.sxbc "$DEST/sx/" 2>/dev/null || true
 # Keep assets dir for Node.js WASM tests