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/SettingsService.swift

@@ -300,6 +300,24 @@ class SettingsService {
         }
     }
 
+    /// Input bar height in points — default 80
+    var inputBarHeight: Double {
+        get { cache["inputBarHeight"].flatMap(Double.init) ?? 80.0 }
+        set {
+            cache["inputBarHeight"] = String(newValue)
+            DatabaseService.shared.setSetting(key: "inputBarHeight", value: String(newValue))
+        }
+    }
+
+    /// Whether the sidebar is visible — default true
+    var sidebarVisible: Bool {
+        get { cache["sidebarVisible"] != "false" }
+        set {
+            cache["sidebarVisible"] = String(newValue)
+            DatabaseService.shared.setSetting(key: "sidebarVisible", value: String(newValue))
+        }
+    }
+
     // MARK: - MCP Permissions
 
     var mcpCanWriteFiles: Bool {