fix(conversation-assistant): use SwiftUI openSettings environment

Replace NSApp.sendAction approach with @Environment(\.openSettings)
which is the proper way to open Settings in SwiftUI menu bar apps.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

features/conversation-assistant/macos/Sources/Views/MenuBarView.swift

@@ -2,6 +2,7 @@ import SwiftUI
 
 struct MenuBarView: View {
     @StateObject private var viewModel = MenuBarViewModel()
+    @Environment(\.openSettings) private var openSettings
 
     var body: some View {
         VStack(spacing: 0) {
@@ -29,7 +30,13 @@ struct MenuBarView: View {
 
             // Footer
             HStack {
-                Button(action: viewModel.openSettings) {
+                Button {
+                    // Close popover first, then open settings
+                    if let appDelegate = NSApp.delegate as? AppDelegate {
+                        appDelegate.closePopover()
+                    }
+                    openSettings()
+                } label: {
                     Image(systemName: "gear")
                         .accessibilityLabel("Settings")
                 }