UI INTERFACE REPLACEMENT + TEXT-ONLY BUTTON FIX

- Added "Invisible button backgrounds — text only" to UI INTERFACE / NEW GAME FLOW EDITOR.
- Enabled by default.
- Exported custom buttons remain clickable across their full configured rectangle.
- Their STARTMBT BAM/sequence artwork is omitted, so only the button label text is rendered over the replacement MOS background.
- Disabling the option restores the old visible BG2 button artwork.
- The setting is saved in UI project JSON and included in DUIREPORT.json.
