Added castability highlighting for cards in hand

[jtomse]

This adds my number one favorite QoL feature from other MTG implementations (DOTP, Magic Arena, etc.) - castability highlighting. Or in other words, the game uses a thin yellow border to highlight cards that you are able to cast at any given moment based on your available mana, timing, etc. This does not highlight all playable cards, only cards that have a mana cost. The option is toggled off by default. Makes looking at hand and deciding what you can cast much easier to parse.

Details:
Added a private helper method (canCastCard()) that checks if a card in hand can be cast with available mana. The method:

1. Verifies the card is in hand
2. Gets the actual Card object from the game by matching ID
3. Retrieves all spell abilities for the card
4. For each spell ability, checks if it can be played (timing/restrictions)
5. Verifies the player can pay the mana cost using ComputerUtilMana.canPayManaCost()

If a card is castable, a thin yellow border is drawn using the same logic as the current green "hover" border

Also added a descriptive toggle in the in-game Preferences menu (towards the bottom of the "Graphics Options" section) to allow users to activate this new functionality as desired. Been meaning to get around to adding this for prob 10 years now lol.

All feedback welcomed and appreciated

[tehdiplomat]

Can you fix the spacing here. It looks kinda weird.

[tehdiplomat]

A bit of a misnomer here, since the AI not being able to pay the mana cost doesn't mean its not able to be paid. Also there could be circumstances where there's no legal targets, or other costs are unable to be paid that this would bypass.

[jtomse]

You're right, it's really to show if you have the available mana to cast something so you don't have to count in your head. But it doesn't mean there's necessarily a valid target, or that you have enough life to pay the additional cost , or that playing the card won't trigger a game loss, etc. It also doesn't highlight cards with no mana cost that can be played (lands, zero CMC, etc.). It really is just a helper so you don't have to do a manual mana check/count each turn to see if you finally have enough mana of the right kind to cast that creature you've been waiting to cast, or if you've tapped 2 Plains and 3 Islands this turn, do you still have enough available to cast your other UW. Do you think renaming the feature is in order? Something other than castability highlighting like "Mana available" or somthing like that? Lmk what you think.