Japanese support and clearer Self-Managed purchase recovery

This update improves Self-Managed purchase recovery and adds Japanese support on Mac and Windows.

• Buying Self-Managed now checks whether another checkout is already pending and offers a clear way to reopen or cancel it.
• Expired checkouts offer sign-in recovery or a fresh start. Purchase checks and cancellation failures show the problem and retry the same action.
• A licence whose device slot is occupied now offers activation management instead of reporting that this device is ready.
• A purchase is marked complete only after payment succeeds and the licence for that purchase is available, even when you already own another licence.
• Purchase recovery reuses a saved device activation after a local save failure and handles an outdated account link.
• Returning from checkout, retrying, or cancelling now preserves the intended purchase and your managed-billing choice.
• Self-Managed trial customers no longer see a managed-subscription cancellation warning when they have no subscription to cancel.
• Japanese is now available for the interface and generated filenames, including menus, notifications and starter Presets. New installations on Japanese systems select Japanese by default; existing language choices are preserved.

This update retains the renaming, watched-folder, shortcut and trial-recovery fixes from 3.0.11.