feat: add in-app Sparkle update logging

- Add published logMessages array to SparkleUpdater to track all update events
- Display logs in the Updates preferences tab with Show/Hide toggle
- Each log entry is timestamped and shows both info and error messages
- Logs persist during session with max 100 entries
- Users can clear logs manually
- Helps diagnose update failures directly in the app UI

Sources/Views/PreferencesView.swift

@@ -257,11 +257,64 @@ private struct UpdatesPreferencesView: View {
                 .foregroundColor(.secondary)
                 .padding(.top, 4)
 
+            Divider()
+                .padding(.vertical, 8)
+
+            Button(action: { sparkleUpdater.showLogs.toggle() }) {
+                Label(sparkleUpdater.showLogs ? "Hide Logs" : "Show Logs", systemImage: "terminal.fill")
+            }
+
+            if sparkleUpdater.showLogs {
+                logsView
+            }
+
             Spacer()
         }
         .toggleStyle(.switch)
         .frame(maxWidth: .infinity, alignment: .leading)
     }
+
+    private var logsView: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text("Update Logs")
+                .font(.caption)
+                .fontWeight(.semibold)
+                .foregroundColor(.secondary)
+
+            ScrollView {
+                VStack(alignment: .leading, spacing: 4) {
+                    if sparkleUpdater.logMessages.isEmpty {
+                        Text("No logs yet. Check for updates to see activity.")
+                            .font(.caption)
+                            .foregroundColor(.secondary)
+                            .italic()
+                    } else {
+                        ForEach(sparkleUpdater.logMessages, id: \.self) { message in
+                            Text(message)
+                                .font(.caption)
+                                .foregroundColor(.secondary)
+                                .lineLimit(3)
+                                .textSelection(.enabled)
+                        }
+                    }
+                }
+                .frame(maxWidth: .infinity, alignment: .leading)
+                .padding(8)
+            }
+            .frame(height: 200)
+            .background(Color(nsColor: .controlBackgroundColor))
+            .cornerRadius(6)
+            .border(.separator, width: 1)
+
+            Button(action: {
+                sparkleUpdater.logMessages.removeAll()
+            }) {
+                Label("Clear Logs", systemImage: "trash")
+                    .font(.caption)
+            }
+            .disabled(sparkleUpdater.logMessages.isEmpty)
+        }
+    }
 }
 
 private struct NotificationsPreferencesView: View {