Fix tvOS focus navigation: add focusSection to all major UI sections

Focus couldn't move from DashboardView controls up to the
CategoryPillBar, or between sections within screens. Added
.platformFocusSection() to:

- ContentView: pill bar and content area as separate focus sections
- DashboardView: header, overview strip, hero+control section
- LeagueCenterView: schedule, standings, leaders, teams sections

This lets the tvOS Focus Engine navigate vertically between all
sections with d-pad up/down.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mlbTVOS/Views/ContentView.swift

@@ -22,6 +22,7 @@ struct ContentView: View {
                 )
                 .padding(.horizontal, DS.Spacing.edgeInset)
                 .padding(.top, navPadTop)
+                .platformFocusSection()
 
                 if showsTicker {
                     ScoresTickerView()
@@ -43,6 +44,7 @@ struct ContentView: View {
                     }
                 }
                 .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
+                .platformFocusSection()
             }
         }
         .task {