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>

shared/static/wasm/sx-platform.js

@@ -463,13 +463,16 @@
       loadLibrary(info.deps[i], loading);
     }
 
+    // Mark as loaded BEFORE executing — self-imports (define-library re-exports)
+    // will see it as already loaded and skip rather than infinite-looping.
+    _loadedLibs[name] = true;
+
     // Load this module
     var ok = loadBytecodeFile("sx/" + info.file);
     if (!ok) {
       var sxFile = info.file.replace(/\.sxbc$/, '.sx');
       ok = loadSxFile("sx/" + sxFile);
     }
-    _loadedLibs[name] = true;
     return !!ok;
   }