Filter hacked submissions from leaderboard views

[SinatrasC]

Summary

• Exclude submissions marked hacked from leaderboard-derived views, summaries, trends, user search, and ranking notifications.
• Check both leaderboard.submission.status and leaderboard.submission_job_status.status so existing and queued hacked markings are hidden from ranking surfaces.
• Bump the ended-leaderboard top-users Redis cache prefix so stale cached rankings are not reused after deploy.
• Add the local fixture schema needed by current leaderboard API tests and cover hacked filtering with a route-level regression test.

Why

• Kernelbot can mark hacked submissions after the fact; kernelboard should stop showing those rows in public ranking surfaces without deleting submission history or run records.

Validation

• ruff check kernelboard/ tests/
• python3 -m py_compile kernelboard/api/leaderboard.py kernelboard/api/leaderboard_summaries.py kernelboard/index.py kernelboard/leaderboard.py ranking_worker.py tests/test_hacked_submission_filters.py tests/api/test_leaderboard_api.py
• REDIS_URL=memory:// uv run --with-requirements requirements.txt pytest tests/api/test_leaderboard_api.py tests/api/test_leaderboard_summaries_api.py tests/test_hacked_submission_filters.py -q
• git diff --check