fix: window close hanging + add confirmation prompt

The onCloseRequested async handler was blocking window close when
save_workspace invoke hung or threw. Fixed with:
1. Confirmation dialog: "Are you sure you want to close Wraith?"
   (only shown if sessions are active, cancel prevents close)
2. Workspace save wrapped in Promise.race with 2s timeout so a
   stuck invoke can never block the close indefinitely

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/layouts/MainLayout.vue

@@ -450,15 +450,28 @@ onMounted(async () => {
     } catch {}
   }, 500);
 
-  // Save workspace on window close (non-fatal)
+  // Confirm close + save workspace on window close
   try {
     const { getCurrentWindow } = await import("@tauri-apps/api/window");
     const appWindow = getCurrentWindow();
-    appWindow.onCloseRequested(async () => {
+    appWindow.onCloseRequested(async (event) => {
+      // Ask for confirmation if there are active sessions
+      if (sessionStore.sessions.length > 0) {
+        if (!confirm("Are you sure you want to close Wraith?")) {
+          event.preventDefault();
+          return;
+        }
+      }
+      // Save workspace before closing (with timeout to prevent hang)
+      try {
         const tabs = sessionStore.sessions
           .filter(s => s.protocol === "ssh" || s.protocol === "rdp")
           .map((s, i) => ({ connectionId: s.connectionId, protocol: s.protocol, position: i }));
-      await invoke("save_workspace", { tabs }).catch(() => {});
+        await Promise.race([
+          invoke("save_workspace", { tabs }),
+          new Promise(resolve => setTimeout(resolve, 2000)),
+        ]);
+      } catch {}
     });
   } catch {}