WASM browser build: interned env keys, async kernel boot, bundled .sx platform

- Symbol interning in sx_types.ml: env lookups use int keys (intern/unintern)
  to avoid repeated string hashing in scope chain walks
- sx-platform.js: poll for SxKernel availability (WASM init is async)
- shell.sx: load sx_browser.bc.wasm.js when SX_USE_WASM=1
- bundle.sh: fix .sx file paths (web-signals.sx rename)
- browser/dune: target byte+js+wasm modes
- Bundle 23 .sx platform files for browser (dom, signals, router, boot, etc.)

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

shared/static/wasm/sx-platform.js

@@ -16,8 +16,7 @@
 (function() {
   "use strict";
 
-  var K = globalThis.SxKernel;
-  if (!K) { console.error("[sx-platform] SxKernel not found"); return; }
+  function boot(K) {
 
   // ================================================================
   // 8 FFI Host Primitives
@@ -234,6 +233,7 @@
     var files = [
       // Spec modules
       "sx/render.sx",
+      "sx/core-signals.sx",
       "sx/signals.sx",
       "sx/deps.sx",
       "sx/router.sx",
@@ -253,6 +253,11 @@
       "sx/adapter-dom.sx",
       // Boot helpers (platform functions in pure SX)
       "sx/boot-helpers.sx",
+      "sx/hypersx.sx",
+      // Test harness (for inline test runners)
+      "sx/harness.sx",
+      "sx/harness-reactive.sx",
+      "sx/harness-web.sx",
       // Web framework
       "sx/engine.sx",
       "sx/orchestration.sx",
@@ -343,4 +348,16 @@
     }
   }
 
+  } // end boot
+
+  // SxKernel is available synchronously (js_of_ocaml) or after async
+  // WASM init. Poll briefly to handle both cases.
+  var K = globalThis.SxKernel;
+  if (K) { boot(K); return; }
+  var tries = 0;
+  var poll = setInterval(function() {
+    K = globalThis.SxKernel;
+    if (K) { clearInterval(poll); boot(K); }
+    else if (++tries > 100) { clearInterval(poll); console.error("[sx-platform] SxKernel not found after 5s"); }
+  }, 50);
 })();