Add Save-State Deletion Shortcut With Confirmation

[RDeckard]

I'm completely new to this project code-wise, but I love NextUI on my Trimui Brick(s): thanks so much for this fantastic OS!

This PR naively tries to tackle #226: it would indeed be great if we could remove Save States! 🙂

Summary

• hook BTN_X into the Save/Load rows so pressing it prompts the user and, if confirmed, deletes the current slot (or reports that it’s already empty)
• introduce Menu_deleteState() to centralize how save-slot files (state, screenshot, disc info) are removed
• add a reusable Menu_confirm() helper so the pause menu can ask for explicit confirmation

Testing

• launch any core, open the in-game menu, populate a save slot
• highlight Save or Load, press X → confirm deletion → slot contents disappear, preview switches to “Empty Slot”
• press X again on the now-empty slot → receive “Slot is already empty.” notice

WDYT?