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>

tests/node/sx-harness.js

@@ -89,7 +89,7 @@ async function createSxEnv(opts = {}) {
   const K = globalThis.SxKernel;
 
   // ---- Load platform (registers FFI, loads .sxbc web stack) ----
-  const platformPath = path.join(WASM_DIR, 'sx-platform-2.js');
+  const platformPath = path.join(WASM_DIR, 'sx-platform.js');
   delete require.cache[require.resolve(platformPath)];
   require(platformPath);