[Runtime Issue]: Mouse focus not captured at runtime

### Build Version

d48b0f1

### Operating System Environment

- [ ] Microsoft Windows (32-bit)
- [ ] Microsoft Windows (64-bit)
- [ ] Mac OS X
- [x] Linux (specify distribution and version below)

### CPU Environment

- [ ] x86 (32-bit Intel/AMD)
- [x] x86\_64 (64-bit Intel/AMD)
- [ ] ARM (32-bit)
- [ ] ARM64 (64-bit; sometimes called AArch64)
- [ ] Other (RISC V, PPC...)

### Game Modes Affected

- [x] Single player
- [ ] Anarchy
- [ ] Hyper-Anarchy
- [ ] Robo-Anarchy
- [ ] Team Anarchy
- [ ] Capture the Flag
- [ ] Bounty
- [ ] Entropy
- [ ] Hoard
- [ ] Monsterball
- [ ] Cooperative

### Game Environment

_No response_

### Description

On startup, mouse cursor does not dissapear to be replaced and controlled by in-game cursor. Desktop cursor and in-game cursor are shown at the same time and desktop cursor is controlled instead.

Game also hung once with this console output upon exit of game:
X Error of failed request: BadWindow (invalid Window parameter)
Major opcode of failed request: 40 (X_TranslateCoords)
Resource id in failed request: 0xe02388
Serial number of failed request: 872
Current serial number in output stream: 872

Running on Ubuntu Mate 24.04.2 using X11

### Regression Status

Probably started with the changeover to SDL3

### Steps to Reproduce

Launch game, main menu loads, but control of in-game cursor is not captured. Keyboard and Joystick inputs are captured as normal.