Error message on sign in is moving when opening the keyboard (iOS)

### Describe the Bug

Just a small style problem:
The error message is moving while opening and closing the keyboard.

https://github.com/karakeep-app/karakeep/blob/1608804f2b5202697197b1b31d51ae89b39cb11b/apps/mobile/app/signin.tsx#L88

While checking online, it seems like KeyboardAvoidingView could be the problem.

### Steps to Reproduce

1. Open app
2. trigger Server address is required error
3. open and close keyboard

### Expected Behaviour

error message shouldn't move

### Screenshots or Additional Context

https://github.com/user-attachments/assets/09635852-4aa6-469f-a65d-a25035d6a39e

### Device Details

iOS

### Exact Hoarder Version

0.23.1

### Have you checked the troubleshooting guide?

- [x] I have checked the troubleshooting guide and I haven't found a solution to my problem

Start by reproducing the issue on iOS using the listed steps, then inspect apps/mobile/app/signin.tsx around line 88 and the KeyboardAvoidingView usage. Done means the “Server address is required” message stays in place while the keyboard opens and closes.

Written by the indexing model from the issue text.