[Feature]: Bind mouse buttons to launch custom apps

### 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

Could you please add a new feature in mouse button customization: allow mapping any mouse button to launch a user-chosen program.
When I select a mouse key, there should be an option to browse and pick an executable. Pressing the button will directly open the selected app.
This would be super useful for quickly opening my daily-used tools with one mouse click. Really appreciate your hard work on OpenLogi!

### Proposed solution

Could you please add a new feature in mouse button customization: allow mapping any mouse button to launch a user-chosen program.
When I select a mouse key, there should be an option to browse and pick an executable. Pressing the button will directly open the selected app.
This would be super useful for quickly opening my daily-used tools with one mouse click. Really appreciate your hard work on OpenLogi!

### Alternatives considered

Could you please add a new feature in mouse button customization: allow mapping any mouse button to launch a user-chosen program.
When I select a mouse key, there should be an option to browse and pick an executable. Pressing the button will directly open the selected app.
This would be super useful for quickly opening my daily-used tools with one mouse click. Really appreciate your hard work on OpenLogi!

### Related area(s)

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

### Additional context

_No response_

Start by locating the mouse button customization and CLI action-handling entry points in the Rust project. Trace how button mappings are stored and executed, then determine where executable selection and launching fit across supported platforms. Done means a user can choose an application for a mouse button and pressing that button launches it reliably.

Written by the indexing model from the issue text.