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/UpdateCheckService.swift

@@ -35,6 +35,11 @@ final class UpdateCheckService {
 
     var updateAvailable: Bool = false
     var latestVersion: String? = nil
+    var downloadURL: URL? = nil
+
+    // Manual check state — drives the update alert in ContentView
+    var isCheckingManually: Bool = false
+    var manualCheckMessage: String? = nil
 
     private let apiURL = "https://gitlab.pm/api/v1/repos/rune/oai-swift/releases/latest"
     private let releasesURL = URL(string: "https://gitlab.pm/rune/oai-swift/releases")!
@@ -48,6 +53,24 @@ final class UpdateCheckService {
         }
     }
 
+    /// Manual check triggered from the Help menu. Non-blocking — result surfaces via manualCheckMessage.
+    func checkForUpdatesManually() {
+        guard !isCheckingManually else { return }
+        isCheckingManually = true
+        Task.detached(priority: .background) {
+            await self.performCheck()
+            let current = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String ?? ""
+            await MainActor.run {
+                if self.updateAvailable, let v = self.latestVersion {
+                    self.manualCheckMessage = String(localized: "Version \(v) is available.")
+                } else {
+                    self.manualCheckMessage = String(localized: "You're up to date (v\(current)).")
+                }
+                self.isCheckingManually = false
+            }
+        }
+    }
+
     private func performCheck() async {
         guard let url = URL(string: apiURL) else { return }
 
@@ -69,9 +92,16 @@ final class UpdateCheckService {
         let latestVer = tagName.hasPrefix("v") ? String(tagName.dropFirst()) : tagName
         let currentVer = Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String ?? "0.0.0"
 
+        // Extract direct DMG download URL from release assets
+        let dmgURL: URL? = (release["assets"] as? [[String: Any]])?
+            .first { ($0["name"] as? String ?? "").lowercased().hasSuffix(".dmg") }
+            .flatMap { $0["browser_download_url"] as? String }
+            .flatMap { URL(string: $0) }
+
         if isNewer(latestVer, than: currentVer) {
             await MainActor.run {
                 self.latestVersion = latestVer
+                self.downloadURL = dmgURL
                 self.updateAvailable = true
             }
         }