Add a git merge conflict simulator (games)

There is a git concepts simulator and a git quiz, but neither covers the thing beginners actually fear.

Shape: a conflict is already on screen with the markers in it. The user resolves it and sees the result, with the repository state visible alongside so the markers stop being mysterious.

Worth covering:

• what <<<<<<<, ======= and >>>>>>> each delimit, and which side is which
• that resolving means editing the file to what you want, not picking a side
• git checkout --ours and --theirs, and that during a rebase they mean the opposite of what you expect
• git merge --abort as the escape hatch
• a conflict that resolves cleanly but is semantically wrong, which is the one that reaches production

Companion to https://devops-daily.com/posts/linux-git-docker-learning-order, which argues Git is best learned by breaking something and getting it back.

Start by locating the existing Git concepts simulator and Git quiz in the TypeScript project and study how their game state and UI are structured. Define the conflict scenarios and repository-state display from this issue, then verify that users can resolve markers, understand ours/theirs and abort behavior, and encounter a semantically wrong clean resolution.