Migrate from Core Data to SwiftData

- Replace Core Data with SwiftData for iOS 18+
- Create MoodEntryModel as @Model class replacing MoodEntry entity
- Create SharedModelContainer for App Group container sharing
- Create DataController with CRUD extensions replacing PersistenceController
- Update all views and view models to use MoodEntryModel
- Update widget extension to use SwiftData
- Remove old Core Data files (Persistence*.swift, .xcdatamodeld)
- Add EntryType enum with all entry type cases
- Fix widget label truncation with proper spacing and text scaling

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Shared/Views/BGView.swift

@@ -6,6 +6,7 @@
 //
 
 import SwiftUI
+import SwiftData
 
 struct BGViewItem: View {
     @AppStorage(UserDefaultsStore.Keys.moodTint.rawValue, store: GroupUserDefaults.groupDefaults) private var moodTint: MoodTints = .Default
@@ -81,13 +82,13 @@ struct BGView: View, Equatable {
 
 struct BGView_Previews: PreviewProvider {
     static var previews: some View {
-        BGView().environment(\.managedObjectContext, PersistenceController.shared.viewContext)
+        BGView().modelContainer(DataController.shared.container)
             .onAppear(perform: {
-                PersistenceController.shared.populateMemory()
+                DataController.shared.populateMemory()
             })
-        
+
         BGView()
             .preferredColorScheme(.dark)
-            .environment(\.managedObjectContext, PersistenceController.shared.viewContext)
+            .modelContainer(DataController.shared.container)
     }
 }