Yes, Joseph Stalin committed War Crimes or Crimes Against Humanity, but not under those specific charges. Charges must be individual and straight to the point, and cannot be generalized.
Being a dictator is not a crime. While being a dictator and committing genocide is a crime.
Negiotiating a Non-agreesion Pact is not a crime, nor could it be charged as a crime.
Stalin did not command troops directly in the Battle of Stalingrad. He did command indirectly.
If you are to charge a person, you have to give specific charges that break humanitarian laws. The given ones do not, and so you cannot charge him based on these.
5. Other (He is not guilty, would be your answer).
This would change, however, if you were to charge him on actual crimes. For example:
1. Execution of political rivals and citizens.
2. Massacres.
3. Usage of gulag system to control the population through fear.
4. Punishing soldiers who do not martydom, and are captured in war.
5. Allowing War Crimes to happen.
6. etc.
if any of these are used, and some which are not named, then you can sentence him. However, the reasons that are given are not enough for him to be punished.