Add suspense, resource, and transitions — Phase 2 complete

- suspense render-dom form: shows fallback while resource loads, swaps
  to body content when resource signal resolves
- resource async signal: wraps promise into signal with loading/data/error
  dict, auto-transitions on resolve/reject via promise-then
- transition: defers signal writes to requestIdleCallback, sets pending
  signal for UI feedback during expensive operations
- Added schedule-idle, promise-then platform functions
- All Phase 2 features now marked Done in status tables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/bootstrap_js.py

@@ -449,6 +449,7 @@ class JSEmitter:
             "dom-focus": "domFocus",
             "try-catch": "tryCatch",
             "error-message": "errorMessage",
+            "schedule-idle": "scheduleIdle",
             "element-value": "elementValue",
             "validate-for-request": "validateForRequest",
             "with-transition": "withTransition",
@@ -3031,6 +3032,11 @@ PLATFORM_ORCHESTRATION_JS = """
 
   function promiseResolve(val) { return Promise.resolve(val); }
 
+  function promiseThen(p, onResolve, onReject) {
+    if (!p || !p.then) return p;
+    return onReject ? p.then(onResolve, onReject) : p.then(onResolve);
+  }
+
   function promiseCatch(p, fn) { return p && p.catch ? p.catch(fn) : p; }
 
   // --- Abort controllers ---
@@ -3474,6 +3480,10 @@ PLATFORM_ORCHESTRATION_JS = """
   function errorMessage(e) {
     return e && e.message ? e.message : String(e);
   }
+  function scheduleIdle(fn) {
+    if (typeof requestIdleCallback !== "undefined") requestIdleCallback(fn);
+    else setTimeout(fn, 0);
+  }
   function elementValue(el) { return el && el.value !== undefined ? el.value : NIL; }
 
   function domAddListener(el, event, fn, opts) {