Update the docs to be uv-native and more onboarding-friendly

[Muhtasham]

Fleshed docs to be

(1) easy way to get familiar w/ codebase, and (2) enable others to use CodeClash

Goal: reduce setup friction and give newcomers a clear path to run and extend CodeClash.

[john-b-yang]

Love the changes @Muhtasham, happy to move to a uv based repository.

My only quibble with this repo - I'm a bit reluctant to change the BattleSnake and HuskyBench/Poker environments, the main reason being backwards compatibility.

We ran a bunch of tournaments, where the environment doesn't use uv. If we change the environment, then the trajectories become "out of sync" with the environments.

Other than that, the documentation changes look fantastic, and uv seems to be the cool thing to use as of late, so let's switch to that.

I'm going to revert the changes to the Dockerfile's of this PR, then approve + squash/merge.

Thanks a bunch!

[john-b-yang]

Ok, just did the revert. For arenas we add going forwards, very happy to use uv for those.