feat(ios): gate Focus tab behind focus_mode_enabled feature flag

ios/ChronoMind/App/ContentView.swift

@@ -47,11 +47,13 @@ struct ContentView: View {
                 }
                 .tag(Tab.timeline)
 
-            PomodoroView()
-                .tabItem {
-                    Label(Tab.focus.rawValue, systemImage: Tab.focus.icon)
-                }
-                .tag(Tab.focus)
+            if FeatureFlagService.shared.isEnabled("focus_mode_enabled") {
+                PomodoroView()
+                    .tabItem {
+                        Label(Tab.focus.rawValue, systemImage: Tab.focus.icon)
+                    }
+                    .tag(Tab.focus)
+            }
 
             HistoryView()
                 .tabItem {
@@ -73,7 +75,10 @@ struct ContentView: View {
         NavigationSplitView {
             // Sidebar
             VStack(spacing: 0) {
-                ForEach(Tab.allCases) { tab in
+                ForEach(Tab.allCases.filter { tab in
+                if tab == .focus { return FeatureFlagService.shared.isEnabled("focus_mode_enabled") }
+                return true
+            }) { tab in
                     Button {
                         selectedTab = tab
                     } label: {