feat: add bracket visualization for tournament schedule (#8)

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.

src/app/admin/tournaments/[id]/page.tsx

@@ -7,6 +7,7 @@ import Navigation from "@/components/Navigation"
 import TeamsSection from "@/components/TeamsSection"
 import { DeleteTournamentButton } from "@/components/DeleteTournamentButton"
 import { ScheduleGenerator } from "@/components/ScheduleGenerator"
+import { BracketVisualization } from "@/components/BracketVisualization"
 import MatchEditor from "@/components/MatchEditor"
 
 interface PageProps {
@@ -420,6 +421,11 @@ export default function TournamentDetailPage({ params }: PageProps) {
           </div>
         )
 
+      case "bracket":
+        return (
+          <BracketVisualization rounds={rounds} />
+        )
+
       default:
         return null
     }
@@ -555,6 +561,18 @@ export default function TournamentDetailPage({ params }: PageProps) {
               >
                 Results
               </button>
+              {hasSchedule && (
+                <button
+                  onClick={() => setActiveTab("bracket")}
+                  className={`whitespace-nowrap py-4 px-1 border-b-2 font-medium text-sm ${
+                    activeTab === "bracket"
+                      ? "border-green-500 text-green-600"
+                      : "border-transparent text-gray-500 hover:text-gray-700 hover:border-gray-300"
+                  }`}
+                >
+                  Bracket
+                </button>
+              )}
               <span className="border-transparent text-gray-400 whitespace-nowrap py-4 px-1 border-b-2 font-medium text-sm cursor-not-allowed">
                 Analytics
               </span>