Adds a visual bracket display showing rounds as columns with matchup cards.
Changes:
- Created BracketVisualization component with CSS grid layout
- Added 'Bracket' tab to tournament detail page (visible when schedule exists)
- Matchup cards show team names, scores, and winner highlighting
- Current round is highlighted with green styling
- Added BDD feature file with 3 scenarios covering bracket display
- Added step definitions for bracket interaction tests
3 scenarios, 24 steps, all passing.
