Implement priority-based scoring system with streaks and monthly leaderboards

[Copilot]

Students are rewarded based on priority: (1) first to solve a problem, (2) optimal solution [reserved for future], (3) daily solve streaks, (4) monthly top 3 rankings.

Scoring Formula

total_points = (100 × difficulty × (2 if first_solve else 1)) + streak_bonus
streak_bonus = 10 × days + (weeks × 1.5 × base)

Examples: 1000-rated problem = 100 pts base, 200 pts if first solve. 7-day streak = 175 pts bonus, 14-day = 560 pts.

Database Changes

• User: current_streak, longest_streak, last_solve_date, monthly_score, last_monthly_reset
• MonthlyLeaderboard: Historical rankings with reward tracking (top 3: $50/$25/$10)
• solves: Added solved_at timestamp for streak calculation

Implementation

• bemo/scoring.py: Centralized scoring logic (update_user_streak, calculate_problem_score, update_monthly_score)
• routes.py: Integrated into submission flow at line 540-569, added /leaderboard route
• Fixed all-time leaderboard query (was ascending, now desc)

UI

Home page - Three-column layout: All-Time, Monthly (with 🥇🥈🥉), Contributors

Leaderboard page - Tabbed view (Monthly/All-Time/Streaks) with scoring documentation

Dashboard - Added current streak (🔥), longest streak, monthly score cards

Migration

Run migrate_scoring_system.py to add new columns and MonthlyLeaderboard table. Idempotent and backward compatible.

Future Work

Time complexity analysis (priority #2) requires Judge0 execution metrics integration - infrastructure prepared in scoring module for cascading rewards (O(n) earns O(n²) points but not O(1)).

See SCORING_SYSTEM.md for API documentation and IMPLEMENTATION_SUMMARY.md for deployment checklist.

Original prompt

Improve the leaderboard and scoring system; students should be rewarded for being the first to solve a problem at a time complexity, finding the optimal solution to a problem, being consistent and solving any problem in a streak, and being in the top 3 of the leaderboard every month in that order of importance. Determining the time complexity of a solution and optimal time complexity should be left for further development. If a student achieved O(n) complexity for example, they should get rewards for O(n^2) and beyond but O(1) should be left open.

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[kushb007]

The scoring system should only apply to the first submission of an open time complexity. Once a time complexity is solves, it and all easier complexities are closed from scoring.