feat: Kisani rebrand, step-based onboarding flow, dark mode fixes

- Rename app to Kisani in all UI text and Face ID prompt
- Replace flat 2-state RootView with 5-step flow: ConnectView →
  LoginView → FolderSetupView → PhotoPermissionView → MainTabView
- Remove NavigationStack from LoginView (was causing nested-stack crash);
  drive navigation via ConnectionStore.isSessionActive
- Add FolderSetupView and PhotoPermissionView onboarding screens with
  step indicator (2/3, 3/3), spring entrance animations, and UGreen
  connection chip
- Fix dark mode button invisibility: PrimaryButtonStyle and PillButtonStyle
  now use AppTheme.inkInverse; GhostButtonStyle border uses ink.opacity(0.25)
- Add AppTheme.inkInverse adaptive token (dark bg ink on dark, white on light)
- Add ConnectionStore.isSessionActive (non-persisted) and
  onboardingPhotoShown (UserDefaults-persisted)
- Add os_log logging in LoginViewModel at auth start/success/failure
- Remove dead Help button from ConnectView
- UGreenCompatibilityBadge, KeychainStore, SavedConnections, extensions,
  PrivacyInfo.xcprivacy, unit test target and test stubs
- AppTheme: full UIColor dynamic provider tokens for dark/light adaptive color
- AppearanceMode enum + segmented picker in SettingsView
- BackupView: enlarged ring, removed options card and linear progress bar
- HistoryView: duration and bytes formatting, improved typography hierarchy

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

Shared/Persistence/KeychainStore.swift

@@ -0,0 +1,48 @@
+import Foundation
+import Security
+
+enum KeychainStore {
+    private static func key(for id: UUID) -> String {
+        "com.nasbackup.connection.\(id.uuidString)"
+    }
+
+    static func savePassword(_ password: String, for id: UUID) {
+        let account = key(for: id)
+        let data = Data(password.utf8)
+
+        let deleteQuery: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrAccount: account
+        ]
+        SecItemDelete(deleteQuery as CFDictionary)
+
+        let addQuery: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrAccount: account,
+            kSecAttrAccessible: kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly,
+            kSecValueData: data
+        ]
+        SecItemAdd(addQuery as CFDictionary, nil)
+    }
+
+    static func loadPassword(for id: UUID) -> String? {
+        let query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrAccount: key(for: id),
+            kSecReturnData: true,
+            kSecMatchLimit: kSecMatchLimitOne
+        ]
+        var result: AnyObject?
+        guard SecItemCopyMatching(query as CFDictionary, &result) == errSecSuccess,
+              let data = result as? Data else { return nil }
+        return String(data: data, encoding: .utf8)
+    }
+
+    static func deletePassword(for id: UUID) {
+        let query: [CFString: Any] = [
+            kSecClass: kSecClassGenericPassword,
+            kSecAttrAccount: key(for: id)
+        ]
+        SecItemDelete(query as CFDictionary)
+    }
+}