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/ui/main_tui/render/mod.rs

@@ -40,6 +40,7 @@ impl MainTui {
             &self.state.downloads,
             self.state.active_downloads_count,
             daemon.as_deref(),
+            self.listener_fallback,
         );
 
         self.render_content(frame, main_chunks[1]);