fix(tray): prevent exit when chat window closes

Switched from Builder::run() to Builder::build() + App::run(event_handler)
so ExitRequested can be intercepted. Without this, the hidden chat window
failing to load localhost:1420 triggered a clean exit and Robin disappeared
from the tray silently.

src-tauri/src/lib.rs

@@ -104,6 +104,14 @@ pub fn run() {
             commands::panel_closed,
             commands::chat,
         ])
-        .run(tauri::generate_context!())
-        .expect("error while running Robin");
+        .build(tauri::generate_context!())
+        .expect("error building Robin")
+        .run(|_app, event| {
+            // Robin lives in the system tray. Prevent the process from exiting
+            // when the chat window is closed or hidden — only the tray "Quit"
+            // menu item should terminate the app.
+            if let tauri::RunEvent::ExitRequested { api, .. } = event {
+                api.prevent_exit();
+            }
+        });
 }