Multiple selfhosted accounts with the same email address

### Steps To Reproduce

I have 2 selfhosted instance. One is my main isntance, the other is a backup that receives a daily upadted based on the main instance. So they have the exact the same content and users.

Adding 2 accounts with DIFFERENT email addresses to the browser plugin works just fine, but adding the same account as from the main stance with the SAME email address does not work. It just overwrites the main instance one. I can only add a second account (selfhosted or not) if the account has a different email than any already added account.

I can observe the exact same behaviour on the mobile app as well.

Side Note: Yes, I am using a third party server, but I setup a test server instance with the official bitwarden server with the same behaviour. This issue is not server related anyway and seems to be only client side.

### Expected Result

I can add multiple accounts with the same email address accross different instances.

### Actual Result

I can only overwrite accounts if they have the same email address.

### Screenshots or Videos

_No response_

### Additional Context

_No response_

### Operating System

Windows

### Operating System Version

win11

### Web Browser

Firefox

### Browser Version

_No response_

### Environment Versions

Version: 2026.8.0 of the broweser plugin
Version: 2026.8.1 of the ios app

### Issue Tracking Info

- [x] I understand that work is tracked outside of Github. A PR will be linked to this issue should one be opened to address it, but Bitwarden doesn't use fields like "assigned", "milestone", or "project" to track progress.

Start by reproducing the account-add flow in the browser plugin and iOS app described in the issue, then trace how accounts are identified and stored when email addresses match. Compare behavior across two self-hosted instances and verify that both accounts remain available without overwriting either one.

Written by the indexing model from the issue text.