What is the ruling on my fasting if I intended to fast but oversleeping prevented me from performing Qiyam al-Layl (night vigil prayer), suhoor (pre-dawn meal), and Witr prayer, knowing that I woke up seconds before the Fajr adhan and prayed Fajr?

If you fast an obligatory fast, such as Ramadan, and you make the intention for it during the night, your fast is valid. It is permissible to pray Witr even if it extends beyond the Fajr adhan, because its time extends from after the 'Isha prayer until the emergence of dawn. If it is not prayed within this time, it should be prayed as a make-up prayer between the emergence of dawn and the Fajr prayer.