I think since this is something movable, building-related air and sun rights aren’t applicable.
The OP also specifies that the airship stays in legal airspace.
So, I think the legal issues are two:
The first is airship-related: can an airship legally follow such a whimsical flight plan? Any thoughts from pilots? [Note that the issue is the same whether or not the person is willing to be shaded]
The second is independent of an airship: Can I legally follow someone around (with an airship or just a giant hand-held parasol) and continually shade them against their will (assuming no trespassing)?
I’m sure there’s no law specifically against it, but it wouldn’t take much for the victim to get this to be considered some kind of criminal harassment. My guess is the first offense would lead to a warning to knock it off rather than jail time, but once the victim got a restraining order, persisting would lead to the kind of pissed of judge that means someone is headed for a little semi-quiet time for reflection with free meals.