Make application validation manual-only

[msaroufim]

What changed

• removed the 22:00 America/Los_Angeles application-validation scheduler and its all-leaderboard scan
• removed the APPLICATION_VALIDATION_ENABLED setting and scheduler startup hooks
• kept validation behind the authenticated admin API/CLI batch operation
• preserved top-10-by-user defaults plus --all-users, --only-missing, --wait, and the two-job concurrency bound
• updated tests and documentation to describe manual-only behavior

Why

Automatic validation would silently expand to every future problem that adds a validation contract, before leaderboard-mode triggering and rate limiting have been designed. Keeping this explicit makes GPU spend and failure handling operator-controlled in the meantime.

Existing validation records and Kernelboard badges are unchanged.

Validation

• uv run ruff check . --exclude examples/ --line-length 120
• uv run pytest -q tests/test_application_validation.py tests/test_admin_api.py tests/test_admin_cli.py tests/test_leaderboard_db.py (120 passed)
• uv run pytest -q -m 'not integration' tests (252 passed, 14 deselected)
• repository-wide search confirms no scheduler symbol, 10pm schedule, or validation-enable environment toggle remains

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/libkernelbot
application_validation.py					26-32
leaderboard_db.py
utils.py
Project Total

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