fix: three robustness bugs outside the friends list

Found in a wider bug audit of the streaming/process-management code.

- Viewer ctrl-c/SIGINT was ignored mid-stream: viewer::run raced the
  cancel token only against listener.accept(), not the bridge itself, so
  once the local player connected nothing checked it. CLI needed a second
  ctrl-c to quit and a GUI "Disconnect" only took effect via the child's 2s
  SIGKILL backstop (and the host saw the viewer ~2s longer). Now races the
  bridge against cancel, mirroring the host's handle_peer. (viewer/mod.rs)

- Wayland portal pipewire fd leaked on a capture-setup error: wayland::start
  into_raw_fd'd the fd and relied on pipeline::spawn's after_spawn hook to
  close it, but setup_audio/gst-spawn can ?-return before the hook runs,
  leaking the fd per failed attempt. Now the OwnedFd is moved into the hook,
  so it's closed whether the hook runs or (on early error) the unused closure
  is dropped. (host/wayland.rs)

- Detached players (mpv/vlc) zombied under the long-lived GUI: spawn_detached
  dropped the std Child, which has no orphan reaping, so each closed player
  left a <defunct> entry until the GUI exited. Now a detached thread wait()s
  it; the setsid'd player still survives a parent exit (init reaps it then).
  A double-fork was avoided deliberately — fork(2) + non-trivial work in this
  multithreaded process is unsound. (common/process.rs)

47 gui / 8 headless tests pass, clippy + fmt clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/viewer/mod.rs

@@ -71,7 +71,18 @@ pub async fn run(ticket: EndpointTicket, opts: ViewerOpts) -> Result<()> {
             accepted = listener.accept() => {
                 let (tcp, peer) = accepted?;
                 tracing::info!(%peer, "local viewer connected");
-                crate::common::tunnel::bridge(quic_send, quic_recv, tcp).await
+                // Race the bridge against ctrl-c so a disconnect lands promptly
+                // mid-stream (mirrors the host's handle_peer). Without this, the
+                // cancel token is set but nothing checks it once the player has
+                // connected — ctrl-c is ignored until a second press, and a GUI
+                // "Disconnect" only takes effect via the child's SIGKILL backstop.
+                tokio::select! {
+                    res = crate::common::tunnel::bridge(quic_send, quic_recv, tcp) => res,
+                    _ = cancel.cancelled() => {
+                        tracing::info!("ctrl-c received during stream — disconnecting");
+                        Ok(())
+                    }
+                }
             }
             _ = cancel.cancelled() => {
                 tracing::info!("ctrl-c received before local viewer connected");