Does a wet dream involving seeing nudity and masturbating in the dream necessitate ghusl (ritual bath), and does it affect the validity of the fast, especially upon waking up during the daytime in Ramadan?

What you saw in your dream is from Satan. To be safe from it, it is recommended to frequently seek refuge in Allah and rely on Him, to consistently recite the remembrance before sleep, to sleep in a state of purity, to avoid thinking about such matters while awake, to refrain from watching obscene images, and to keep good company. Ghusl is only required upon the emission of manī (spermatic fluid), and fasting is valid during the day in Ramadan whether manī is emitted or not.