[Feature]: 鼠标按键设置自定义

### 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

MX Anywhere 3S鼠标的前进后退设置，只能在默认菜单里选。比如我想将某一键设置成打开某个文件夹，无法设置。即使修改Config.toml。也会报错。

### Proposed solution

鼠标的按键设置可增加自定义操作。

### Alternatives considered

_No response_

### Related area(s)

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

### Additional context

_No response_

Start by examining the current mouse button settings and how Config.toml is parsed, since the issue reports that custom values currently cause an error. Define the supported custom actions, including opening a folder, and verify that a remapped button can execute one successfully.

Written by the indexing model from the issue text.