This PR introduces cross-platform support for launching external binaries (`ace-lm` and `ace-synth`) on Windows systems.
**Key changes:**
* Introduced `EXE_EXT` constant in `AceStepWorker.h` using `Q_OS_WIN` macro to handle `.exe` extensions automatically.
* Updated binary path construction to ensure `QFileInfo::isExecutable()` and `QProcess` work correctly on Windows.
* The code remains fully compatible with Linux/macOS (extension remains empty).
**Why this is needed:**
On Windows, `QProcess` and `QFileInfo` require the `.exe` suffix to correctly identify and execute binary files. Without this change, the application fails to find the required tools even if they are present in the directory.
