teker821/ULTRAKILL ? reverse-engineered prompt

I want you to help me build a playable ULTRAKILL style game prototype in C#, using the code in this repo as the base.

It should feel like a fast first person shooter with movement, jumping, dashing, shooting, melee, parrying, style ranks, enemies, bosses, a simple menu, options, checkpoints, and a level select flow. Keep it focused on gameplay and systems, since this repo does not include the original art, models, or textures, so use placeholders where needed.

Please wire up the core player controls, combat, enemy behavior, HUD, and basic game progression so it can actually be played end to end. If anything important is missing or unclear, look up current docs online if you need to and make reasonable choices. Also make sure the code stays organized and easy to extend, since I may want to add more weapons, enemies, and levels later.