fix: preserve SFTP session on language switch

Save and restore live SFTP session when switching languages
instead of disconnecting and recreating everything from scratch.
Terminal reconnects automatically via set_server().

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/app.py

@@ -171,9 +171,15 @@ class App(ctk.CTk):
         # Use provided key or default to first tab
         current_key = restore_tab_key or self._tab_keys[0]
 
-        # Disconnect terminal and SFTP before destroying tabs
+        # Save live SFTP session before destroying tabs
+        saved_sftp = self.files_tab._sftp
+        saved_sftp_path = self.files_tab._remote_path
+        saved_sftp_alias = self.files_tab._current_alias
+        saved_local_path = self.files_tab._local_path
+        self.files_tab._sftp = None  # Prevent disconnect on destroy
+
+        # Disconnect terminal before destroying tabs
         self.terminal_tab._disconnect()
-        self.files_tab._disconnect_sftp()
 
         # Detach tab contents
         self.terminal_tab.pack_forget()
@@ -219,9 +225,28 @@ class App(ctk.CTk):
         except Exception:
             pass
 
-        # Restore server selection
+        # Restore SFTP session without reconnecting
+        if saved_sftp and saved_sftp.connected:
+            self.files_tab._sftp = saved_sftp
+            self.files_tab._current_alias = saved_sftp_alias
+            self.files_tab._remote_path = saved_sftp_path
+            self.files_tab._local_path = saved_local_path
+            self.files_tab._set_remote_buttons_state("normal")
+            self.files_tab._remote_status.configure(
+                text=t("connected_sftp").format(alias=saved_sftp_alias)
+            )
+            self.files_tab._refresh_local()
+            self.files_tab._refresh_remote()
+        elif alias:
+            # No live session — reconnect via server selection
+            self.files_tab.set_server(alias)
+
+        # Restore server selection for other tabs
         if alias:
-            self._on_server_select(alias)
+            self.terminal_tab.set_server(alias)
+            self.info_tab.set_server(alias)
+            self.keys_tab.set_server(alias)
+            self.totp_tab.set_server(alias)
 
         # Update sidebar
         self.sidebar.update_language()