[Feature Request] Small Quality of life improvements

[Tosskek]

1. Add a “Duplicate input/output folder” checkbox.
   When enabled, the output folder should automatically match the input folder — so the user doesn’t need to specify it manually every time.

2. Allow the “Open output folder” button to remain clickable during rendering.
   Currently it becomes greyed out, making it impossible to open the folder once rendering has started.

3. Enable double-clicking the preview window to open the output file in an external video player (e.g., MPV).
   This would allow users to watch the video while it’s still rendering. I typically use MKV, which plays fine during rendering.
   Right now I have to manually find the file in the file explorer — a direct option from the preview window would be much more convenient.

With these changes, the workflow becomes simple and robust: drag and drop a video, enable “duplicate input/output folder,” double-click the preview to open it in the external player, and watch the file while it renders — without needing to use the file explorer.

Thank you.

[TNTwise]

All of these have been requested before, but as of recent I havent had time to touch RVE's code. Updates will be very slow until the end of the year.