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/CaseraQLPreview/PreviewViewController.swift

@@ -198,16 +198,15 @@ class PreviewViewController: UIViewController, QLPreviewingController {
     func preparePreviewOfFile(at url: URL) async throws {
         print("CaseraQLPreview: preparePreviewOfFile called with URL: \(url)")
 
-        // Parse the .casera file
+        // Parse the .casera file — single Codable pass to detect type, then decode
         let data = try Data(contentsOf: url)
+        let decoder = JSONDecoder()
 
-        // Detect package type first
-        if let json = try? JSONSerialization.jsonObject(with: data) as? [String: Any],
-           let typeString = json["type"] as? String,
-           typeString == "residence" {
+        let envelope = try? decoder.decode(PackageTypeEnvelope.self, from: data)
+
+        if envelope?.type == "residence" {
             currentPackageType = .residence
 
-            let decoder = JSONDecoder()
             let residence = try decoder.decode(ResidencePreviewData.self, from: data)
             self.residenceData = residence
             print("CaseraQLPreview: Parsed residence: \(residence.residenceName)")
@@ -218,7 +217,6 @@ class PreviewViewController: UIViewController, QLPreviewingController {
         } else {
             currentPackageType = .contractor
 
-            let decoder = JSONDecoder()
             let contractor = try decoder.decode(ContractorPreviewData.self, from: data)
             self.contractorData = contractor
             print("CaseraQLPreview: Parsed contractor: \(contractor.name)")
@@ -287,6 +285,13 @@ class PreviewViewController: UIViewController, QLPreviewingController {
     }
 }
 
+// MARK: - Type Discriminator
+
+/// Lightweight struct to detect the package type without a full parse
+private struct PackageTypeEnvelope: Decodable {
+    let type: String?
+}
+
 // MARK: - Data Model
 
 struct ContractorPreviewData: Codable {