Update gemini version to 2.5-flash in firebaseai

[YoungHypo]

[YoungHypo]

Please define constants, as suggested by Gemini.

As for a more long-term solution, I will add this to the PRD.

Thanks for your suggestion! I’ve first made a new file at Constants/ModelNames.swift. I’m also very interested in the Remote Config and recognize its value as a long-term solution. If possible, I’d love to explore it further and contribute to this area. @peterfriese