feat: add confirmation prompt before closing active session tabs (#793)

Shows a toast confirmation when closing terminal, RDP, VNC or telnet
tabs to prevent accidental session loss from misclicks.

src/ui/locales/en.json

@@ -385,6 +385,9 @@
     "newTab": "New Tab",
     "splitScreen": "Split Screen",
     "closeTab": "Close Tab",
+    "confirmClose": "Close this active session?",
+    "close": "Close",
+    "cancel": "Cancel",
     "sshManager": "SSH Manager",
     "hostManager": "Host Manager",
     "cannotSplitTab": "Cannot split this tab",