Feature request: Could you please add a frame/mask overlay feature, like the real‑DS‑bezel effect shown in my screenshot.
Detailed requirements:
1. Add bezel/mask overlay, render the NDS shell border around top & bottom screens, just like the attached picture.
2. For both top screen and bottom screen, support independent X‑axis / Y‑axis offset adjustment, move screen position freely.
3. Scale setting: use integer‑based multiplier, adjustable in **0.1 step increments** for each screen separately.
4. All layout parameters (offset X/Y, scale factor, mask toggle) should be savable per‑game profile.
This is very useful for TV mode, so I can precisely place two DS screens and wrap them inside DS‑style bezel.
Thank you very much for your great work on this Switch port!