Add token functionality for encrypted app tickets

[ghost]

This PR adds support for using pre-generated encrypted app tickets via a token in configs.user.ini.

Changes:

• Adds Base64 decoding functionality
• Adds token field and loading method in Settings class
• Modifies GetEncryptedAppTicket to first try using the token from configs.user.ini
• Falls back to normal ticket generation if no token is found
• Updates README with usage instructions

This allows users to provide their own encrypted app tickets without modifying the emulator code, which is useful for games that require specific ticket formats or when using tickets generated by the real Steam client.

Implementation details:

• Token must be Base64-encoded (valid tickets start with 'CAI' after encoding)
• Added 2 new files: base64.h and base64.cpp
• Modified: settings.h, settings.cpp, steam_user.cpp, and README.md

Tested with sample tokens and verified that games requiring valid encrypted tickets launch successfully.

[DogancanYr]

Can you prepare a sample file?
Also, I don't think it works in dave the diver.

[ghost]

Dave The Diver has StubDRM and that has nothing to do with this PR, sorry.

[DogancanYr]

Dave The Diver has StubDRM and that has nothing to do with this PR, sorry.

What exactly does it work for?
(It can open Re4 with denuvo drm.)

[ndiruhniu]

Works with Stellar Blade. Thank you.

[ghost]

Thanks for verifying! :)

[ghost]

deleted old repo - new PR will be added soon with encrypted savegame swap and hybrid steamclient as well