feat(tui): say so in the status bar when the listener took another port

With the login screen's own attempts no longer holding the port, a
session listens somewhere other than the configured port mainly when
another program already holds it. soulseek-rs still falls back to an
ephemeral port there, which is what lets several clients on one machine
share a configured port, and it advertises the port it really bound. A
manual port forward on the router then points at nothing, though, and
the TUI never said so; the CLI already warns.

After login the TUI compares the bound port with the configured one,
using the CLI's rule, and the status bar's title reads "port X in use,
listening on Y" for the rest of the session. A window attached to a
daemon shows nothing: the daemon owns its listener.

Nicotine+ keeps retrying the configured port every five seconds and
Soulseek.NET refuses it; neither falls back. Keeping the fallback and
making it visible is a deliberate difference.

soulseek-rs/src/run.rs

@@ -502,14 +502,17 @@ fn run_default_tui(
         // Best-effort: make ourselves reachable behind a home router so
         // firewalled peers can connect back. Mapped only once the listener is
         // up, and for the port it really bound. Kept alive for the session.
-        let _port_mapper = outcome
-            .client
-            .listen_port()
-            .map(crate::port_mapping::PortMapper::spawn);
+        let bound_port = outcome.client.listen_port();
+        let _port_mapper =
+            bound_port.map(crate::port_mapping::PortMapper::spawn);
 
         let store = crate::persist::paths::state_dir()
             .map(crate::persist::state::StateStore::new);
 
+        let listener_fallback = bound_port
+            .filter(|&bound| listen_port != 0 && bound != listen_port)
+            .map(|bound| (listen_port, bound));
+
         let exit = launch_main_tui(
             terminal,
             Arc::new(outcome.client),
@@ -517,6 +520,7 @@ fn run_default_tui(
             Duration::from_secs(resolved.search_timeout),
             store,
             config_path.clone(),
+            listener_fallback,
         )
         .map_err(|e| CliError::new(Exit::Failure, e.to_string()))?;
 
@@ -592,6 +596,7 @@ fn run_attached_tui(
         Duration::from_secs(resolved.search_timeout),
         None,
         config_path,
+        None,
     )
     .map(|_| ())
     .map_err(|e| CliError::new(Exit::Failure, e.to_string()))