fix(sdk): reset syncOnce dedup on uid transition to undefined

The loginWithToken wrap clears creds via Accounts._unstoreLoginToken() +
Meteor.connection.setUserId(null), which does NOT fire Accounts.onLogout.
Without resetting lastSyncedUid on the resulting uid=undefined transition,
a subsequent re-login (e.g. e2ee-passphrase-management's loginByUserState
of the same user) is deduped and runUserDataSync never runs — the page
stays wedged on PageLoading and the Login button never hides.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ggazzo

apps/meteor/client/startup/startup.ts

@@ -57,7 +57,17 @@ const runUserDataSync = async (uid: string) => {
 // false and the page stuck on PageLoading.
 let lastSyncedUid: string | undefined;
 const syncOnce = (uid: string | undefined): void => {
-	if (!uid || uid === lastSyncedUid) return;
+	// Reset on logout transitions so a subsequent re-login (same uid or different)
+	// runs a fresh sync. Force-logout via the SDK loginWithToken wrap clears
+	// creds via Accounts._unstoreLoginToken() + setUserId(null), which does NOT
+	// fire Accounts.onLogout — so without this branch, lastSyncedUid stays set,
+	// the next login is deduped, runUserDataSync is skipped, and
+	// useUserDataSyncReady stays false (page wedged on PageLoading).
+	if (!uid) {
+		lastSyncedUid = undefined;
+		return;
+	}
+	if (uid === lastSyncedUid) return;
 	lastSyncedUid = uid;
 	void runUserDataSync(uid).catch((err) => {
 		console.warn('[startup] runUserDataSync failed; clearing dedup to allow a retry', err);