add offline banner, sync status indicators

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

Apps/MagnumOpus/ContentView.swift

@@ -35,12 +35,46 @@ struct ContentView: View {
 				messages: viewModel.messages
 			)
 		}
+		.safeAreaInset(edge: .bottom) {
+			statusBanner
+		}
 		.task {
 			await viewModel.syncNow()
 			viewModel.startPeriodicSync()
 		}
 	}
 
+	@ViewBuilder
+	private var statusBanner: some View {
+		switch viewModel.syncState {
+		case .error(let message):
+			HStack {
+				Image(systemName: "wifi.slash")
+				Text("Offline — showing cached mail")
+				Spacer()
+				Button("Retry") {
+					Task { await viewModel.syncNow() }
+				}
+				.buttonStyle(.borderless)
+			}
+			.font(.caption)
+			.padding(8)
+			.background(.yellow.opacity(0.2))
+		case .syncing(let mailbox):
+			HStack {
+				ProgressView()
+					.controlSize(.small)
+				Text("Syncing\(mailbox.map { " \($0)" } ?? "")…")
+					.font(.caption)
+				Spacer()
+			}
+			.padding(8)
+			.background(.blue.opacity(0.1))
+		case .idle:
+			EmptyView()
+		}
+	}
+
 	private func connectAccount() {
 		guard let (config, credentials) = accountSetup.buildConfig() else { return }
 		do {