v4.8.3: Clear SonarCloud new-code issues

Fixes the 4 reported bugs and ~97 code smells flagged in the new-code
period. No behavior changes.

Bugs (swift:S3923) — DomainInspectionService's confidenceFor* helpers each
returned `error == nil ? .low : .low`, an inert conditional. Simplified to
`return .low` and dropped the now-unused `error` parameter.

Smells:
- Merged 14 identical `.empty`/`.error` switch branches in DomainViewModel
- Consolidated duplicate implementations (clearPresentedResults/reset,
  String.nonEmpty/nilIfEmpty, ExportFormat.id/fileExtension)
- Extracted nested ternaries into TLSGrade.tone, EmailSecurityGrade.tone,
  and ChangeImpactClassification.color; removed ContentView.impactColor
  and the duplicate mapping in BatchResultsView
- Documented empty closures and singleton inits
- Marked unused protocol-conformance parameters `_`
- Renamed CloudSyncTrigger.`import` to `imported` (raw value preserved)
  and SSLSessionDelegate's _serverTrust/_tlsMetadata
- Merged nested ifs in the DER parser; flattened closure nesting in
  PortScanService and IntegrationService
- Replaced two-case switches with if/else

Left open: S107 (init parameter counts), S115 (constants mirroring DoH and
ipapi JSON keys), S1075 (false positives on https:// literals), and two
S117 hits on SwiftUI $binding shorthand. These want a Won't Fix resolution
in SonarCloud, not a code change.

1 files changed, 2 insertions, 4 deletions

diff --git a/DomainDig/PurchaseService.swift b/DomainDig/PurchaseService.swift
index d31afc7..4ab8ef4 100644
--- a/DomainDig/PurchaseService.swift
+++ b/DomainDig/PurchaseService.swift
@@ -288,12 +288,10 @@ final class PurchaseService {
 
     private func storeMessage(for error: Error, fallback: String) -> String {
         if let storeKitError = error as? StoreKitError {
-            switch storeKitError {
-            case .networkError:
+            if case .networkError = storeKitError {
                 return "The App Store is offline right now."
-            default:
-                return fallback
             }
+            return fallback
         }
 
         let message = error.localizedDescription.trimmingCharacters(in: .whitespacesAndNewlines)