Implement Linux Build Script (`build-linux.js`)

[ZFordDev]

Summary

Create a dedicated Linux build script to unify AppImage, deb, and future Snap logic.

Tasks

• Call metadata injection
• Run electron-builder with Linux targets
• Add Snap detection hooks (Linux Packaging Cleanup #118)
• Ensure artifact naming matches package.json Build Section Cleanup #120
• Document WSL limitations (for Documentation Overhaul (Build + Updater) #122)

Branch

issue/115-build-system-modernisation → issue/119-build-script-redesign