[Docs] BUG_HUNT_ANSWER_KEY.md is committed alongside the intentionally seeded bug issues

[grantfox-oss]

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Why this matters
BUG_HUNT_ANSWER_KEY.md sits at the repo root and, based on its name, appears to catalog intentionally introduced bugs used to seed contributor issues. If it stays in the default branch it risks spoiling the exercise for contributors who browse the repo before picking up an issue.

Acceptance criteria

• Confirm whether BUG_HUNT_ANSWER_KEY.md should remain public
• If it should stay, gate it behind a maintainers-only branch or move it to a less discoverable location
• If it should be public, add a note in README.md explaining its purpose

Files to touch

• BUG_HUNT_ANSWER_KEY.md
• README.md

Out of scope
Removing individual bug entries.