fix: defer child-store root disposal to avoid nested cleanNode

disposeDirectory called a createRoot dispose() synchronously. When
triggered by pinForOwner's onCleanup during a parent remount (e.g.
switching to a WSL server re-keys the ServerKey Show), the inner
dispose ran a nested cleanNode cascade on a sibling root while the
outer cascade was mid-traversal, corrupting solid-js's graph walk
state and surfacing as TypeError: Cannot read properties of null
(reading '1') at chunk-*.js:992 after ~155 recursive cleanNode frames.

Queue the dispose on a microtask so synchronous bookkeeping still
runs (map deletes, onDispose cache invalidation) but the reactive
cleanup happens after the outer traversal finishes.

packages/app/src/context/global-sync/child-store.ts

@@ -96,8 +96,15 @@ export function createChildStoreManager(input: {
     lifecycle.delete(directory)
     const dispose = disposers.get(directory)
     if (dispose) {
-      dispose()
       disposers.delete(directory)
+      // Defer the actual solid-js root disposal. When disposeDirectory runs
+      // from pinForOwner's onCleanup during a parent remount, calling
+      // dispose() here triggers a nested cleanNode cascade on the inner
+      // root while the outer cascade is mid-traversal, which corrupts
+      // solid-js's graph walk state and throws `Cannot read properties of
+      // null (reading '1')` at chunk-*.js:992. Running dispose on a
+      // microtask lets the outer cleanup finish first.
+      queueMicrotask(dispose)
     }
     delete children[directory]
     input.onDispose(directory)