Fix treasure selector filtering and improve tests

[Korgys]

Summary

• correct the README typo in the project description
• ensure the treasure selector builds its item pool from the filtered list that excludes enemy-specific loot
• fix the TODO comment spelling in ArminService and add a regression test covering the item pool filtering logic

Testing

• dotnet test (fails: dotnet CLI is not available in the execution environment)

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https://chatgpt.com/codex/tasks/task_e_68c85ab982548330b62d7ad9a853a24e