fix: release instance lock before spawning updated client

crates/client/src/main.rs

@@ -719,6 +719,8 @@ async fn handle_message(
                 display::cmd_done("🔄", "update", "", true, "updated — restarting");
                 // Delete old binary
                 let _ = std::fs::remove_file(&old);
+                // Release single-instance lock so new process can start
+                release_instance_lock();
                 // Restart with same args (new console window on Windows)
                 let args: Vec<String> = std::env::args().skip(1).collect();
                 #[cfg(target_os = "windows")]