feat: prompt command (MessageBox), admin status in banner

crates/common/src/protocol.rs

@@ -15,6 +15,14 @@ pub struct WindowInfo {
 pub enum ServerMessage {
     /// Request a screenshot from the client
     ScreenshotRequest { request_id: Uuid },
+    /// Show a MessageBox on the client asking the user to do something.
+    /// Blocks until the user clicks OK — use this when you need the user
+    /// to perform a manual action before continuing.
+    PromptRequest {
+        request_id: Uuid,
+        message: String,
+        title: Option<String>,
+    },
     /// Execute a shell command on the client
     ExecRequest {
         request_id: Uuid,