As for your question, Michael. The Manifest file is used to tell the system where to find the Main method that starts the application. Without it the application will not start when you type:
I also presume that I should not pack a properties file into the JAR file I will submit ([spec] "The JAR file must have the following layout and contents in its root:").
This makes me believe the examiner will extract runme.jar and run the programs in the console.
When you submit your assignment, each part (client and server) must be executable using a command of this exact form:
java -jar <path_and_filename> [<mode>]