Add Smart data checking mode

Shared/DataRefreshMode.swift

@@ -0,0 +1,24 @@
+import Foundation
+
+enum DataRefreshMode: String, CaseIterable, Identifiable {
+    case standard
+    case smart
+
+    var id: String { rawValue }
+
+    var displayName: String {
+        switch self {
+        case .standard: return "Standard"
+        case .smart: return "Smart"
+        }
+    }
+
+    var summary: String {
+        switch self {
+        case .standard:
+            return "Saves battery. Refreshes price data up to twice daily."
+        case .smart:
+            return "Checks for newer data more often in the background and refreshes full prices only when an update is available."
+        }
+    }
+}