Replace onboarding flow with silent v1 import and iCloud alert

Delete the multi-page onboarding sheet. On first launch the app now
silently imports any v1 instances from UserDefaults (splitting embedded
basic-auth credentials out of the URL and into the Keychain) and then,
if the device is signed in to iCloud, shows a single alert offering to
enable sync. Accepting shows a blocking progress overlay until the
initial upload completes.

Yattee/Views/Settings/DeveloperSettingsView.swift

@@ -176,15 +176,6 @@ struct DeveloperSettingsView: View {
         #if !os(tvOS)
         notificationTestingSection
         #endif
-
-        Section {
-            Button {
-                NotificationCenter.default.post(name: .showOnboarding, object: nil)
-                appEnvironment?.navigationCoordinator.dismissSettings()
-            } label: {
-                Label(String(localized: "settings.advanced.showOnboarding"), systemImage: "hand.wave")
-            }
-        }
     }
 
     @ViewBuilder

Yattee/Views/Settings/MigrationImportRow.swift

@@ -0,0 +1,126 @@
+//
+//  MigrationImportRow.swift
+//  Yattee
+//
+//  Reusable row component for displaying a legacy import item.
+//
+
+import SwiftUI
+
+struct MigrationImportRow: View {
+    let item: LegacyImportItem
+    let onToggle: () -> Void
+
+    var body: some View {
+        Button(action: onToggle) {
+            HStack(spacing: 12) {
+                // Checkbox
+                Image(systemName: item.isSelected ? "checkmark.circle.fill" : "circle")
+                    .font(.title2)
+                    .foregroundStyle(item.isSelected ? Color.accentColor : .secondary)
+
+                // Instance type icon
+                instanceIcon
+                    .font(.title2)
+                    .foregroundStyle(.secondary)
+                    .frame(width: 28)
+
+                // Instance details
+                VStack(alignment: .leading, spacing: 2) {
+                    Text(item.displayName)
+                        .font(.body)
+                        .foregroundStyle(.primary)
+
+                    Text(item.url.host ?? item.url.absoluteString)
+                        .font(.caption)
+                        .foregroundStyle(.secondary)
+                        .lineLimit(1)
+                }
+
+                Spacer()
+
+                // Reachability indicator
+                reachabilityIndicator
+            }
+            .padding(.vertical, 8)
+            .contentShape(Rectangle())
+        }
+        .buttonStyle(.plain)
+    }
+
+    // MARK: - Subviews
+
+    @ViewBuilder
+    private var instanceIcon: some View {
+        switch item.instanceType {
+        case .invidious:
+            Image(systemName: "server.rack")
+        case .piped:
+            Image(systemName: "cloud")
+        default:
+            Image(systemName: "globe")
+        }
+    }
+
+    @ViewBuilder
+    private var reachabilityIndicator: some View {
+        switch item.reachabilityStatus {
+        case .unknown:
+            EmptyView()
+        case .checking:
+            ProgressView()
+                .controlSize(.small)
+        case .reachable:
+            Image(systemName: "checkmark.circle.fill")
+                .foregroundStyle(.green)
+        case .unreachable:
+            Image(systemName: "exclamationmark.triangle.fill")
+                .foregroundStyle(.orange)
+        }
+    }
+}
+
+// MARK: - Preview
+
+#Preview {
+    List {
+        MigrationImportRow(
+            item: LegacyImportItem(
+                id: UUID(),
+                legacyInstanceID: "test",
+                instanceType: .invidious,
+                url: URL(string: "https://invidious.example.com")!,
+                name: "My Invidious",
+                isSelected: true,
+                reachabilityStatus: .reachable
+            ),
+            onToggle: {}
+        )
+
+        MigrationImportRow(
+            item: LegacyImportItem(
+                id: UUID(),
+                legacyInstanceID: "test2",
+                instanceType: .piped,
+                url: URL(string: "https://piped.example.com")!,
+                name: nil,
+                isSelected: false,
+                reachabilityStatus: .unreachable
+            ),
+            onToggle: {}
+        )
+
+        MigrationImportRow(
+            item: LegacyImportItem(
+                id: UUID(),
+                legacyInstanceID: "test3",
+                instanceType: .invidious,
+                url: URL(string: "https://another.invidious.com")!,
+                name: "Another Instance",
+                isSelected: true,
+                reachabilityStatus: .checking
+            ),
+            onToggle: {}
+        )
+    }
+}