Generate a deck of cards in Clojure / Clojurescript
There are a few minor improvements you can make here that lead to a fairly elegant implementation.

First, using flatten is rarely a good idea, because rather than just dealing with the top-level structure of the thing you hand it, it reaches down into its inner structure, thus making it brittle when you change the representation of your data. Therefore, you should instead use apply concat in place of flatten in your code.

However, as @ChrisMurphy points out, the for macro already supports list products, so you can replace the usage of flatten or apply concat and the two usages of for with a single usage of for that produces a flat sequence.

Then, instead of writing out the full range of numbers from 1 to 13, you can use the range function to replace that vector with (range 1 (inc 13)) or something equivalent.

Finally, rather than manually deconstructing and reconstructing each map in your lambda that you pass to map-indexed, you can use the assoc function to simply add the :card-id mapping.

With these changes, you end up with a solution that looks like this:

(defn new-deck []
  (map-indexed
   #(assoc %2 :card-id (inc %1))
   (for [suit [:spade :heart :diamond :club]
         rank (range 1 (inc 13))]
     {:suit suit :rank rank})))