The broken konstant-fire interaction should be forbidden in code

[blackshadowshade]

The broken konstant-fire interaction is described in #1802.

PoshFrosh has asked here whether this could be documented in the code base.

We currently have BMButton->validate_recipe() which checks for valid recipes, it would make sense to add a restriction here.

[PoshFrosh]

@dwvanstone brought up a few important considerations in chat regarding potential loopholes where Fire (F) and Konstant (k) could still interact unexpectedly. If we ultimately decide to restrict F and k from coexisting in the same recipe, a simple restriction rule between those two skills won't be enough.

To completely prevent F and k interactions, we would also need to address the following edge cases:

The Doppelganger Dice issue:

1. Ban D() and k() in the same recipe
   A Doppelganger die could copy an opponent's Fire die, turning into an F() and introducing F and k into the same recipe mid-game.
2. Ban D() and F() in the same recipe
   A Doppelganger die could copy an opponent's Fire die, turning into an F() and introducing F and k into the same recipe mid-game.

The Auxiliary Dice issue:

3. Ban +D() [Doppelganger auxiliary dice]
   Adding a Doppelganger die to an opponent’s recipe that already contains k() or F() creates the same Doppelganger risk outlined above.
4. Ban +F() [Fire auxiliary dice]
   Adding a Fire die as an auxiliary die to an opponent’s button can inject F() into a recipe that already contains k().
5. Ban +k() [konstant auxiliary dice]
   Adding a Konstant die as an auxiliary die to an opponent’s button can inject k() into a recipe that already contains F().

No buttons currently exist in production with any of these combos.
In "staging only" I found the following:
Iowa contains both D() and k()
blackshadowshade contains both D() and k()
blackshadowshade contains both D() and F()