Add Center Stage support alongside MijickCamera

Center Stage is a device-level Apple feature that works independently
of any camera framework. Added:

- Center Stage button in top control bar (person.crop.rectangle icon)
- checkCenterStageAvailability() checks device.activeFormat.isCenterStageSupported
- toggleCenterStage() uses AVCaptureDevice.isCenterStageEnabled
- Button only appears on devices that support Center Stage
- Yellow highlight when enabled

Works with MijickCamera since Center Stage is controlled at the
AVCaptureDevice level, not the camera view level.

SelfieRingLight/Features/Camera/ContentView.swift

@@ -2,6 +2,7 @@ import SwiftUI
 import MijickCamera
 import Bedrock
 import Photos
+import AVFoundation
 
 struct ContentView: View {
     @State private var settings = SettingsViewModel()
@@ -15,6 +16,10 @@ struct ContentView: View {
     @State private var capturedVideoURL: URL?
     @State private var showPostCapturePreview = false
     
+    // Center Stage support
+    @State private var isCenterStageAvailable = false
+    @State private var isCenterStageEnabled = false
+    
     var body: some View {
         GeometryReader { geometry in
             let maxRingSize = calculateMaxRingSize(for: geometry)
@@ -65,6 +70,9 @@ struct ContentView: View {
             }
         }
         .ignoresSafeArea()
+        .onAppear {
+            checkCenterStageAvailability()
+        }
         .sheet(isPresented: $showPaywall) {
             ProPaywallView()
         }
@@ -86,6 +94,22 @@ struct ContentView: View {
     
     private var topControlBar: some View {
         HStack {
+            // Center Stage button (only shown when available)
+            if isCenterStageAvailable {
+                Button {
+                    toggleCenterStage()
+                } label: {
+                    Image(systemName: isCenterStageEnabled ? "person.crop.rectangle.fill" : "person.crop.rectangle")
+                        .font(.body)
+                        .foregroundStyle(isCenterStageEnabled ? .yellow : .white)
+                        .padding(Design.Spacing.small)
+                        .background(.ultraThinMaterial, in: Circle())
+                }
+                .accessibilityLabel(String(localized: "Center Stage"))
+                .accessibilityValue(isCenterStageEnabled ? "On" : "Off")
+                .accessibilityHint(String(localized: "Keeps you centered in frame"))
+            }
+            
             Spacer()
             
             // Grid toggle
@@ -115,6 +139,28 @@ struct ContentView: View {
         }
     }
     
+    // MARK: - Center Stage
+    
+    /// Checks if Center Stage is available on this device
+    private func checkCenterStageAvailability() {
+        // Center Stage requires a compatible device (iPad with A12+ or some iPhones)
+        guard let device = AVCaptureDevice.default(.builtInWideAngleCamera, for: .video, position: .front) else {
+            isCenterStageAvailable = false
+            return
+        }
+        
+        // Check if the device supports Center Stage
+        isCenterStageAvailable = device.activeFormat.isCenterStageSupported
+        isCenterStageEnabled = AVCaptureDevice.isCenterStageEnabled
+    }
+    
+    /// Toggles Center Stage on/off
+    private func toggleCenterStage() {
+        AVCaptureDevice.centerStageControlMode = .app
+        AVCaptureDevice.isCenterStageEnabled.toggle()
+        isCenterStageEnabled = AVCaptureDevice.isCenterStageEnabled
+    }
+    
     // MARK: - Post Capture View
     
     @ViewBuilder