Wow no... sure haven't. If you use low voltage ones you could use a smart relay to turn them all on or off, or a smart outlet to just shut off the transformer. But solar... I'm gonna guess you won't find anything like that at all. It might be possible to crack one open and see how much spare room there is in there. You MIGHT be able to fit a smart relay in there. But the chances of getting a smart relay that works with the right voltage and still fits inside the housing... meh.
Not sure which country you're in? There seem to be quite a lot options in the UK for post-cap lights, but unfortunately none that are smart. But could you get a standard post-cap light and put a smart bulb in it? I guess it depends on the size of the light and the bulb, but potentially an option if you can't find an all-in-one solution
Probably the closest thing I can think of to your request is the Sylvania Gardenspot lights. Granted they aren't post lights, but I don't think there are any smart lights that I would classify a post light.
Maybe depending upon your deck, router a groove in the underside of one the horizontal rails, or in the corner posts at the stairs and other important points. Use RGBW strip lights with a diffuser channel to make things look pretty. The RGB strips are available with outdoor (IP rated) coating, and the diffuser channels are fairly inexpensive and look nice and would add additional weatherproofing. Using this method, you get a nice glow over the whole deck instead of spots of light.
I stole this from the 'net, but it is basically what I am thinking of.