fix(installer): improve error message when port 4000 is already in use

Replace .unwrap() on TcpListener::bind with .with_context() so users
see a clear message about the port conflict instead of a panic.

Fixes #906

installer/src/tplink.rs

@@ -346,9 +346,13 @@ async fn tplink_launch_telnet_v5(admin_ip: &str) -> Result<(), Error> {
             admin_ip: admin_ip.to_owned(),
         });
 
-    let listener = tokio::net::TcpListener::bind("127.0.0.1:4000")
+    let bind_addr = "127.0.0.1:4000";
+    let listener = tokio::net::TcpListener::bind(bind_addr)
         .await
-        .unwrap();
+        .with_context(|| format!(
+            "Failed to bind to {bind_addr}. Is another process using this port?\n\
+             Try closing any application that might be listening on port 4000 and rerun the installer."
+        ))?;
 
     println!("Listening on http://{}", listener.local_addr().unwrap());
     println!("Please open above URL in your browser and log into the router to continue.");