[Feature]: AppImage package release (Linux)

### 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

Currently the only way to install on linux is through rpm or deb packages. Which limits to certain distribution, isn't portable and the easiest to auto update / install.

AppImages releases would make any linux distro compatible (even if not intended), would allow portable executable, would make it possible to easily install / contain / uninstall or manage the binary and auto update (with the likes of gear lever).

### Proposed solution

Make a build output for an AppImage package (amd64 and arm64)

### Alternatives considered

Flatpak (not available and more complex to package, especially with low level control that openlogi needs with the devices)

RMP and DEB packages are ok, but not easy to have auto update, latest and uninstall compared to an appimage. Plus they are usually distro dependent and do not play nice in many edge cases.

### Related area(s)

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

### Additional context

_No response_

Start by reviewing the existing RPM and DEB packaging and the Linux release build configuration to understand how architecture-specific artifacts are produced. Add AppImage outputs for Linux amd64 and arm64, then verify that each artifact is portable and supports the intended installation and update workflow.

Written by the indexing model from the issue text.