Add Bluetooth status alerts (#385)

- Add alert UI to notify users when Bluetooth is off/unauthorized
- Monitor Bluetooth state changes in BluetoothMeshService
- Show appropriate messages for different Bluetooth states
- Add Settings button to open system settings on iOS
- Check initial Bluetooth state on app startup

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Views/ContentView.swift

@@ -7,6 +7,9 @@
 //
 
 import SwiftUI
+#if os(iOS)
+import UIKit
+#endif
 
 // MARK: - Supporting Types
 
@@ -227,6 +230,18 @@ struct ContentView: View {
             
             Button("cancel", role: .cancel) {}
         }
+        .alert("Bluetooth Required", isPresented: $viewModel.showBluetoothAlert) {
+            Button("Settings") {
+                #if os(iOS)
+                if let url = URL(string: UIApplication.openSettingsURLString) {
+                    UIApplication.shared.open(url)
+                }
+                #endif
+            }
+            Button("OK", role: .cancel) {}
+        } message: {
+            Text(viewModel.bluetoothAlertMessage)
+        }
         .onDisappear {
             // Clean up timers
             scrollThrottleTimer?.invalidate()