chore: wire up AutoFill extension target and rebrand bundle prefix

Adds the AutoFill Credential Provider Extension target (App Group +
Keychain Sharing capabilities, autofill-credential-provider
entitlement), removes the leftover SwiftData bootstrap from
MyPassApp.swift now that Item.swift is gone, and switches the bundle
ID / App Group / Keychain group prefix from com.christophevila to
org.antiloop222 to match the project's existing identifier.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WYqycDFsynHH9VnnK7LNSf

MyPass/MyPassApp.swift

@@ -6,27 +6,12 @@
 //
 
 import SwiftUI
-import SwiftData
 
 @main
 struct MyPassApp: App {
-    var sharedModelContainer: ModelContainer = {
-        let schema = Schema([
-            Item.self,
-        ])
-        let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
-
-        do {
-            return try ModelContainer(for: schema, configurations: [modelConfiguration])
-        } catch {
-            fatalError("Could not create ModelContainer: \(error)")
-        }
-    }()
-
     var body: some Scene {
         WindowGroup {
             ContentView()
         }
-        .modelContainer(sharedModelContainer)
     }
 }