v0.2.1

Added

• Play / Stop button (also Space) in the top bar — audition the spectrogram you see, either the original audio or the watermarked mix, so you can confirm the watermark really is inaudible before exporting.
• Chroma key masking: new Background / mask → Chroma key… option with a color picker. Remove any color (not just white or black) from the source image. The active key is stored per preset.
• File → Recent files: the last eight audio files you opened are persisted in settings.json and available from a new File menu (with Open audio…, Export…, Exit, and Clear list).
• Export — quick-action dialog: after writing a file, offer Open in Audacity (auto-detects Windows install paths and PATH) and Show in folder (uses explorer /select,… on Windows, open / xdg-open elsewhere).

Changed

• Help → Keyboard shortcuts… now lists the Space play/stop shortcut.
• Presets serialize the new chroma_rgb field; older presets still load unchanged.