[Feature]: Sync between devices / import & export settings

### Pre-flight checklist

- [x] I searched existing issues and the [Roadmap](https://github.com/AprilNEA/OpenLogi#roadmap), and this isn't already tracked.

### Problem / motivation

I have two PC users. From what I can tell, I would need to redo all my settings on each user.

### Proposed solution

Provide an export/import config button!

### Alternatives considered

Account (not very local/private focused of course)

### Related area(s)

- [ ] GUI
- [ ] CLI
- [ ] Button actions / remapping
- [ ] DPI
- [ ] SmartShift
- [ ] Per-application profiles
- [x] Configuration (TOML)
- [ ] Auto-update
- [ ] Other

### Additional context

_No response_

No files or tests are named. Start by locating the existing TOML configuration handling and the settings UI entry points, then determine how configuration can be exported and imported locally. Done should include usable import/export controls and preservation of settings across the round trip.

Written by the indexing model from the issue text.