Remove reactive class/style (CSSX covers it), add error boundaries + resource

Reactive class/style (:class-map, :style-map) removed — CSSX components
already handle dynamic class/style via defcomp with full SX logic.

Added:
- error-boundary render-dom form: try/catch around children, renders
  fallback fn with (err retry) on failure, disposes partial effects
- resource async signal: wraps promise into signal with loading/data/error
  states, transitions automatically on resolve/reject
- try-catch, error-message, promise-then platform functions
- Updated Phase 2 status tables and demo page numbering

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

shared/sx/ref/bootstrap_js.py

@@ -411,6 +411,7 @@ class JSEmitter:
             "engine-init": "engineInit",
             # engine orchestration platform
             "promise-resolve": "promiseResolve",
+            "promise-then": "promiseThen",
             "promise-catch": "promiseCatch",
             "abort-previous": "abortPrevious",
             "track-controller": "trackController",
@@ -446,6 +447,8 @@ class JSEmitter:
             "prevent-default": "preventDefault_",
             "stop-propagation": "stopPropagation_",
             "dom-focus": "domFocus",
+            "try-catch": "tryCatch",
+            "error-message": "errorMessage",
             "element-value": "elementValue",
             "validate-for-request": "validateForRequest",
             "with-transition": "withTransition",
@@ -3465,6 +3468,12 @@ PLATFORM_ORCHESTRATION_JS = """
   function preventDefault_(e) { if (e && e.preventDefault) e.preventDefault(); }
   function stopPropagation_(e) { if (e && e.stopPropagation) e.stopPropagation(); }
   function domFocus(el) { if (el && el.focus) el.focus(); }
+  function tryCatch(tryFn, catchFn) {
+    try { return tryFn(); } catch (e) { return catchFn(e); }
+  }
+  function errorMessage(e) {
+    return e && e.message ? e.message : String(e);
+  }
   function elementValue(el) { return el && el.value !== undefined ? el.value : NIL; }
 
   function domAddListener(el, event, fn, opts) {