Add notice if agent isn't running (#47)

* Add agent checker
* Check on foreground

Secretive/Preview Content/PreviewAgentStatusChecker.swift

@@ -0,0 +1,12 @@
+import Foundation
+import Combine
+
+class PreviewAgentStatusChecker: AgentStatusCheckerProtocol {
+
+    let running: Bool
+
+    init(running: Bool = true) {
+        self.running = running
+    }
+
+}