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/bootstrap_vm.py

@@ -75,6 +75,8 @@ SKIP = {
     # JIT dispatch + active VM (platform-specific)
     "*active-vm*", "*jit-compile-fn*",
     "try-jit-call", "vm-call-closure",
+    # Module execution (thin wrappers over native execute_module)
+    "vm-execute-module", "vm-resume-module",
     # Env access (used by env-walk)
     "env-walk", "env-walk-set!",
     # CEK interop