fix: correct model success rate calculation and detection

[BleakNarratives]

This PR fixes a bug in the "Code City Apocalypse" dashboard where the "Sectors Cleared" metric (and the "Model Success Rates" chart) incorrectly counted all unique challenge attempts as successes.

Key changes:

1. Success Detection: Updated the is_event_success helper to recognize successful flag submissions in the archive dataset by checking the flag_found_last_attempt_flag column.
2. Leaderboard Refactor: Modified render_apocalypse_metrics to filter the failure data for successful rows before aggregating unique challenges per model.
3. Zero-Success Visibility: Implemented a merge with the list of unique models to ensure models with zero successful sectors are still displayed on the leaderboard, providing a more accurate performance overview.
4. Linting: Addressed a minor Pythonic iteration warning in the monster assignment logic.

Verified via Playwright screenshots and passed ruff and mypy checks.

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PR created automatically by Jules for task 1364947910522008593 started by @BleakNarratives

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[gemini-code-assist]

Code Review

This pull request updates the event success criteria, simplifies dictionary key iteration, and refines the apocalypse metrics leaderboard to include models with zero successes. Feedback was provided to improve the leaderboard data processing by handling potential null model names and ensuring consistent integer types for sector counts.