Update copyright year

[zabidenhtf]

Updated year to 2026

[petitlapin]

Hi,
thanks for the changes! I would prefer we investigate the way to have the texts directly displayed via SDL_ttf than updating the images. It's a bad design from the initial version I would get rid of for multiple reasons:

• we have no idea on what the strings are
• using a binary file for all the images is not the more secured way in Li-Ri. Any could put any malicious intent on the file and there would be no way to validate if the file is correct or not.

So first "easy" step could be to add the SDL_ttf library as dependency and display the copyright directly. Then a second step would be to have all the texts displayed by SDL_ttf and the last step would be to add internationalisation handling via gettext.
Another step would be to move the generation of all the images from povray in cmake too and in the original Li-Ri repository.

I created petitlapin/Li-Ri#84 which is my vision on how to handle properly the first step.

[petitlapin]

I guess there is also a mix-up between the PR (#2 and #3). Regarding "Options" vs "Mods", I would prefer to keep "Options". It could be "Configuration" or "Settings". For me, a "Mods" is when we update the initial behaviour of the game. For example, it would be if instead of a train we have a plane, more or less boosts.
Changing the language or setting the volume is part of the initial game and is not an external (not from the developers) change of the game.