Fix sync race: return in-flight promise from syncSnapshot so welcome handler waits for actual sync completion

When syncSnapshot() was called while a sync was already in-flight, it
returned immediately (resolved promise) after setting pending=true.
This meant the onServerWelcome handler's SET_PROJECT_EXPANDED dispatch
ran against an empty store before projects were populated.

Now syncSnapshot() returns the in-flight syncPromise when syncing=true,
so callers actually wait for the sync to complete before proceeding.

Author: cursoragent

apps/web/src/routes/__root.tsx

@@ -149,20 +149,25 @@ function EventRouter() {
       }
     };
 
-    const syncSnapshot = async () => {
+    let syncPromise: Promise<void> = Promise.resolve();
+
+    const syncSnapshot = (): Promise<void> => {
       if (syncing) {
         pending = true;
-        return;
+        return syncPromise;
       }
       syncing = true;
-      try {
-        pending = false;
-        await flushSnapshotSync();
-      } catch {
-        // Keep prior state and wait for next domain event to trigger a resync.
-      } finally {
-        syncing = false;
-      }
+      syncPromise = (async () => {
+        try {
+          pending = false;
+          await flushSnapshotSync();
+        } catch {
+          // Keep prior state and wait for next domain event to trigger a resync.
+        } finally {
+          syncing = false;
+        }
+      })();
+      return syncPromise;
     };
 
     void syncSnapshot().catch(() => undefined);