fix(build): resolve Xcode 26 compilation errors

- Add ServerConfigView stub (referenced in SilverAppleApp.swift)
- Add HardeningListView stub (referenced in DashboardView.swift)
- Fix .accentColor → Color.accentColor (ShapeStyle removed member)
- Fix withCheckedThrowingContinuation explicit type annotation
- Make AppEnvironment.serverUrl internal for ServerConfigView access

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SilverApple/App/AppEnvironment.swift

@@ -12,7 +12,7 @@ final class AppEnvironment: ObservableObject {
     let apiClient:    SilverAPIClient
     let mdmService:   MDMEnrollmentService
 
-    private var serverUrl: String {
+    var serverUrl: String {
         UserDefaults.standard.string(forKey: "silverapple.serverUrl") ?? ""
     }
 

SilverApple/Auth/PassportAuthService.swift

@@ -28,7 +28,7 @@ final class PassportAuthService: NSObject, ObservableObject, ASWebAuthentication
 
         let authUrl = buildAuthURL(challenge: challenge)
 
-        let callbackUrl = try await withCheckedThrowingContinuation { continuation in
+        let callbackUrl: URL = try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<URL, any Error>) in
             let session = ASWebAuthenticationSession(url: authUrl, callbackURLScheme: "silverapple") { url, error in
                 if let error { continuation.resume(throwing: error); return }
                 guard let url else { continuation.resume(throwing: AuthError.noCallback); return }

SilverApple/Hardening/Views/HardeningListView.swift

@@ -0,0 +1,16 @@
+import SwiftUI
+
+struct HardeningListView: View {
+    var body: some View {
+        NavigationStack {
+            List {
+                Section {
+                    Label("Privacy hardening checks coming soon.", systemImage: "lock.shield")
+                        .foregroundStyle(.secondary)
+                        .font(.subheadline)
+                }
+            }
+            .navigationTitle("Hardening")
+        }
+    }
+}

SilverApple/Onboarding/Views/MDMEnrollmentView.swift

@@ -15,7 +15,7 @@ struct MDMEnrollmentView: View {
             VStack(spacing: 32) {
                 Image(systemName: "iphone.badge.play")
                     .font(.system(size: 56))
-                    .foregroundStyle(.accentColor)
+                    .foregroundStyle(Color.accentColor)
 
                 VStack(spacing: 12) {
                     Text("Device Management")

SilverApple/Settings/Views/ServerConfigView.swift

@@ -0,0 +1,29 @@
+import SwiftUI
+
+struct ServerConfigView: View {
+    @EnvironmentObject var env: AppEnvironment
+
+    var body: some View {
+        NavigationStack {
+            List {
+                Section("Server") {
+                    HStack {
+                        Text("URL")
+                        Spacer()
+                        Text(env.serverUrl.isEmpty ? "Not configured" : env.serverUrl)
+                            .foregroundStyle(.secondary)
+                            .lineLimit(1)
+                            .truncationMode(.middle)
+                    }
+                }
+
+                Section {
+                    Button("Sign Out", role: .destructive) {
+                        env.authService.signOut()
+                    }
+                }
+            }
+            .navigationTitle("Settings")
+        }
+    }
+}