fix(core): only rebind timelines when late arrivals were actually detected

The late-bind polling was unconditionally rebinding on its first
check even when all timelines were already present, causing visual
regressions across style-prod tests. Now tracks sawMissing flag —
only rebinds if the poll previously detected missing timelines that
subsequently appeared. Compositions with synchronous timeline
registration exit the poll immediately with no side effects.

packages/core/src/runtime/init.ts

@@ -1471,6 +1471,7 @@ export function initSandboxRuntimeModular(): void {
         postState(true);
 
         let lateBindChecks = 0;
+        let sawMissing = false;
         const lateBindInterval = setInterval(() => {
           if (++lateBindChecks > 50) {
             clearInterval(lateBindInterval);
@@ -1482,10 +1483,11 @@ export function initSandboxRuntimeModular(): void {
             const id = hosts[i].getAttribute("data-composition-id");
             if (id && !timelines[id]) {
               allBound = false;
+              sawMissing = true;
               break;
             }
           }
-          if (allBound && lateBindChecks > 1) {
+          if (allBound && !sawMissing) {
             clearInterval(lateBindInterval);
             return;
           }