Add Team Ranking Badges and Baseline Test Coverage
Description:
This merge request introduces ranking badge support and adds foundational test coverage across key modules.
What’s included
- Added rank badge assets (rank1.svg to rank6.svg) into a single canonical location: badges/.
- Updated leaderboard badge loading to use the consolidated badge directory in team_leaderboard.py.
- Added/updated baseline test cases in tests/ for core logic paths (batch processing, project/activity utilities, leaderboard helpers, and schema-oriented checks).
Notes
- Source/business logic files were kept mostly untouched except required badge-loading path update.
- Test suite currently focuses on foundational coverage and can be expanded in follow-up MRs for deeper edge-case validation.