fix(linux): allow dead credentials_ready_tx field without gtk feature

Linux CI clippy (-D warnings) failed on dead_code: TrayShared.credentials_ready_tx is read only from the GTK sign-in callback, but is constructed unconditionally, so a non-gtk build (what CI compiles) leaves it write-only. This is the intended behavior — without the gtk feature there is no GUI sign-in and the daemon relies on its secret-store poll — so gate the field with #[cfg_attr(not(feature = "gtk"), allow(dead_code))]. macOS clippy never caught it because linux.rs is cfg(target_os="linux").

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Adron

linux-ubuntu/crates/tray-app/src/linux.rs

@@ -65,6 +65,11 @@ struct TrayShared {
     /// True when the user has paused sync manually.
     paused: bool,
     /// Fires when sign-in succeeds; the daemon listens on the other end.
+    /// Only read from the GTK sign-in callback (`open_signin`). Without the
+    /// `gtk` feature there is no GUI sign-in, so the daemon relies solely on
+    /// its secret-store poll and this sender is intentionally never fired —
+    /// allow the resulting dead field in that build configuration.
+    #[cfg_attr(not(feature = "gtk"), allow(dead_code))]
     credentials_ready_tx: Option<tokio::sync::oneshot::Sender<()>>,
 }