PNG UI assets for SCENE_CAMERA_SCAN overlay.

Files:
- ok.png / ok_48.png : success icon (neon check)
- bad.png / bad_48.png : failure icon (neon cross)
- scanlines.png : subtle scanlines tile (16x16 RGBA)
- reticle.png : reticle overlay (256x256 RGBA)

These are provided for easy customization. The default firmware UI uses embedded LVGL image descriptors.
