Add gemini 3 pro image

[reynaldichernando]

hi team, making this issue for adding the new nano banana pro (gemini 3 pro image) model

some tasks i can think of:

update our driver detection to include the model
https://github.com/HeyPuter/puter/blob/main/src/puter-js/src/modules/AI.js#L919

add it to our backend service

puter/src/backend/src/modules/puterai/GeminiImageGenerationService.js

Line 42 in f6139bc

'gemini-2.5-flash-image-preview': {

plus i think we need to add it to cost map and etc