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/EmbeddingService.swift

@@ -71,7 +71,7 @@ enum EmbeddingProvider {
 // MARK: - Embedding Service
 
 final class EmbeddingService {
-    static let shared = EmbeddingService()
+    nonisolated static let shared = EmbeddingService()
 
     private let settings = SettingsService.shared
 
@@ -281,7 +281,7 @@ final class EmbeddingService {
     // MARK: - Similarity Calculation
 
     /// Calculate cosine similarity between two embeddings
-    func cosineSimilarity(_ a: [Float], _ b: [Float]) -> Float {
+    nonisolated func cosineSimilarity(_ a: [Float], _ b: [Float]) -> Float {
         guard a.count == b.count else {
             Log.api.error("Embedding dimension mismatch: \(a.count) vs \(b.count)")
             return 0.0