UI redesign Phase 1: NavigationSplitView with collapsible sidebar

- Replace root VStack with NavigationSplitView (2-column, collapsible sidebar)
- Add SidebarView: new chat button, conversation search, list with swipe actions
- Slim HeaderView to text-only (provider + model + star); remove all icon rows
- Move status pills (Online, MCP, Synced) to footer right side
- Remove version number and shortcut hints from footer
- Add resizable InputBar with drag handle (persisted height) and globe/network.slash online toggle
- Fix Norwegian menu appearing on English systems (CFBundleLocalizations in Info.plist)
- Add View menu (Model Info, History, Stats, Credits, Online Mode toggle ⌘⇧O)
- Add ⌘L as alias for Search Conversations (muscle memory for /load users)
- Add Check for Updates to Help menu with download URL from Gitea API
- Add one-time Intel/Rosetta deprecation warning on first launch
- Swift 6: fix self.Self.isoString() call sites in DatabaseService

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

oAI/Services/EncryptionService.swift

@@ -29,7 +29,7 @@ import CryptoKit
 import IOKit
 
 class EncryptionService {
-    static let shared = EncryptionService()
+    nonisolated static let shared = EncryptionService()
 
     private let salt = "oAI-secure-storage-v1" // App-specific salt
     private lazy var encryptionKey: SymmetricKey = {
@@ -41,7 +41,7 @@ class EncryptionService {
     // MARK: - Public Interface
 
     /// Encrypt a string value
-    func encrypt(_ value: String) throws -> String {
+    nonisolated func encrypt(_ value: String) throws -> String {
         guard let data = value.data(using: .utf8) else {
             throw EncryptionError.invalidInput
         }
@@ -55,7 +55,7 @@ class EncryptionService {
     }
 
     /// Decrypt a string value
-    func decrypt(_ encryptedValue: String) throws -> String {
+    nonisolated func decrypt(_ encryptedValue: String) throws -> String {
         guard let data = Data(base64Encoded: encryptedValue) else {
             throw EncryptionError.invalidInput
         }