PM-5370 - return winner placement

[vas3a]

This pull request updates the campus leaderboard report to track and display all placements (not just wins) for Topcoder challenges, and adds tests to ensure non-winning placements are correctly handled. The changes also clarify the definition of a "win" in the leaderboard logic.

Leaderboard SQL logic updates:

• The CTE previously named member_wins is renamed to member_placements and now includes all placements, not just first place. The logic for determining a "win" is updated to check for placement = 1 instead of filtering at the SQL level.
• The participation CTE and all related joins are updated to use member_placements instead of member_wins, ensuring all placements are considered throughout the report. [1] [2]
• The won field in the leaderboard output is now computed as win.member_id IS NOT NULL AND win.placement = 1, so only first-place finishes are counted as wins, while other placements are still tracked.

Test coverage improvements:

• Added a test to verify that non-winning placements (such as 2nd and 3rd place) are returned and correctly represented in the leaderboard results.