Would what I did—delaying the prayer after waking up from sleep and performing a scrupulous ablution—be considered an intentional act to miss the Fajr prayer?

You erred by being negligent in performing the prayer until its time elapsed. However, repentance is obligatory and erases what came before it. You must regret what occurred from you and not return to it, and strive against intrusive thoughts and turn away from them.