Harden iOS app with audit fixes, UI consistency, and sheet race condition fixes

Applies verified fixes from deep audit (concurrency, performance, security,
accessibility), standardizes CRUD form buttons to Add/Save pattern, removes
.drawingGroup() that broke search bar TextFields, and converts vulnerable
.sheet(isPresented:) + if-let patterns to safe presentation to prevent
blank white modals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/Casera/CaseraBundle.swift

@@ -12,7 +12,5 @@ import SwiftUI
 struct CaseraBundle: WidgetBundle {
     var body: some Widget {
         Casera()
-        CaseraControl()
-        CaseraLiveActivity()
     }
 }