SecurityException on addAccountExplicitly after app update — AuthenticatorService not yet registered

## Description

After an app update, `UserAccountManager.createAccount()` crashes with a `SecurityException` on `accountManager.addAccountExplicitly()` because the Android OS has not yet re-registered the app's `AuthenticatorService`.

This is a race condition between the app launching after an update and the OS recognizing the updated authenticator. It occurs sporadically in production — we see it in Crashlytics on multiple devices.

## Stack Trace

```
java.lang.SecurityException: caller uid XXXXX is different than the authenticator's uid
at android.os.Parcel.createExceptionOrNull(Parcel.java:3057)
at android.os.Parcel.createException(Parcel.java:3041)
at android.accounts.AccountManager.addAccountExplicitly(AccountManager.java:892)
at com.salesforce.androidsdk.accounts.UserAccountManager.createAccount(UserAccountManager.java:446)
```

## Root Cause

In `UserAccountManager.createAccount()`, `accountManager.addAccountExplicitly()` is called once with no error handling for `SecurityException`. After an app update, Android may not have re-registered the authenticator yet, causing a UID mismatch.

## Expected Behavior

`addAccountExplicitly()` should retry with a short backoff to allow the OS to register the authenticator:

```java
SecurityException lastException = null;
int maxRetries = 3;
for (int attempt = 0; attempt < maxRetries; attempt++) {
try {
success = accountManager.addAccountExplicitly(acc, password, new Bundle());
break;
} catch (SecurityException e) {
lastException = e;
if (attempt < maxRetries - 1 && Looper.myLooper() != Looper.getMainLooper()) {
Thread.sleep(500);
}
}
}
if (lastException != null) throw lastException;
```

## Affected Versions

- Confirmed on **13.2.0** and **13.2.1**
- Likely affects all versions using Android AccountManager

## Environment

- Android SDK 13.2.0/13.2.1
- Various Android versions (seen on Android 13, 14, 15)
- Occurs after app updates via Play Store or side-loading

Start in UserAccountManager.java at createAccount(), around the accountManager.addAccountExplicitly() call shown in the stack trace, and inspect how authenticator registration is handled after an update. Reproduce or exercise the post-update account-creation path, then verify that a temporary SecurityException no longer causes an unrecovered crash and that the retry behavior is bounded.

Written by the indexing model from the issue text.