[Feature]: Configurable gesture swipe sensitivity / threshold

### 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

The current gesture swipe threshold feels too high, especially for horizontal Left/Right gestures on MX Master mice.

It would be useful to expose the gesture swipe threshold as a configurable setting, either globally or, ideally, separately for horizontal and vertical gestures.

For example:

```toml
[gestures]
horizontal_threshold = 25
vertical_threshold = 50
```

Horizontal gestures are particularly affected because moving the mouse sideways while holding the thumb Gesture Button naturally has a smaller and less comfortable range of motion.

A GUI sensitivity slider would be ideal, but a config.toml option would already solve the problem.

### Proposed solution

As described above

### Alternatives considered

_No response_

### Related area(s)

- [x] 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 gesture swipe threshold implementation and the TOML configuration entry point; then trace how GUI settings are represented. Done means horizontal and vertical thresholds can be configured, with the existing gesture behavior using those values.

Written by the indexing model from the issue text.