Add build-all.sh, bytecode test mode — 5 failures with SX_TEST_BYTECODE=1

The hydration bug root cause: .sxbc bytecoded modules break effect
closures. Source-loaded modules work (15/15), bytecoded fail (10/15).

Run: SX_TEST_BYTECODE=1 node hosts/ocaml/browser/test_wasm_native.js

Failing: scoped static class, signal attr initial, reactive-spread,
CSSX in island scope, reactive attr update.

Also adds build-all.sh (full WASM pipeline) and sx_build target="wasm"
MCP tool integration.

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

hosts/ocaml/browser/test_wasm_native.js

@@ -196,6 +196,12 @@ async function main() {
     K.eval('(do (define test-set-attr (fn (el name val) (effect (fn () (dom-set-attr el name val))))) (let ((el (dom-create-element "div" nil))) (test-set-attr el "class" "from-define") (dom-get-attr el "class")))'),
     'from-define');
 
+  // Verify the effect body ACTUALLY EXECUTES (not just returning a value).
+  // In browser WASM, the effect body silently doesn't run.
+  assert('define+effect body executes',
+    K.eval('(do (define test-fx-log (fn (el log) (effect (fn () (append! log "ran") (dom-set-attr el "class" "fx"))))) (let ((el (dom-create-element "div" nil)) (log (list))) (test-fx-log el log) (str (len log) ":" (first log))))'),
+    '1:ran');
+
   // Same thing with let works (proves it's define-specific)
   assert('let+effect+host-obj',
     K.eval('(let ((test-set-attr (fn (el name val) (effect (fn () (dom-set-attr el name val)))))) (let ((el (dom-create-element "div" nil))) (test-set-attr el "class" "from-let") (dom-get-attr el "class")))'),