fix(cc): include zero-second challenge solves

[DevaanshPathak]

Summary

• include completed progress rows whose solve duration is exactly zero seconds
• preserve zero as a valid per-challenge average in the Command Center template
• add regression coverage for zero, non-zero, and missing durations plus actual template rendering

Root cause

The statistics helper and template both used truthiness checks for solve durations. Challenge completion stores elapsed time as an integer, so a legitimate sub-second solve becomes 0 and was treated as if the value were missing.

Impact

Fast solves now contribute to average solve-time statistics instead of biasing averages upward. Challenges with a valid zero-second average display 0m rather than a missing-value marker.

Testing

• uv run pytest tests/unit/apps/cc/test_challenges.py — 3 passed
• uv run pytest tests/unit/apps — 16 passed
• uv run black --check tests/unit/apps/cc/test_challenges.py
• uv run isort --check-only finbot/apps/cc/routes/challenges.py tests/unit/apps/cc/test_challenges.py

Fixes #556

[Copilot]

Pull request overview

Fixes Command Center challenge statistics and rendering so legitimate 0-second solve durations are treated as valid values (not missing), ensuring fast solves contribute to averages and zero averages render as 0m instead of a missing marker.

Changes:

• Update _challenge_list_with_stats to include completed rows where completion_time_seconds == 0 by filtering on is not None.
• Update the CC challenges template to render averages when avg_solve_seconds is 0 (distinguishing None vs 0).
• Add regression tests covering zero, non-zero, and missing durations, including a real template render assertion.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
finbot/apps/cc/routes/challenges.py	Fixes stats calculation to include zero-second completed solves in average computation.
finbot/apps/cc/templates/pages/challenges.html	Renders 0m for a valid zero average by checking is not none rather than truthiness.
tests/unit/apps/cc/test_challenges.py	Adds unit/regression coverage for the zero-duration edge case and template rendering.

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