v1.8.2: session management hardening

- Fix infinite reconnect loop in terminal (_send_to_shell guard)
- Safe language switch: disconnect + reconnect instead of object transplant
- Improved SFTP reconnect flow with proper validation
- Add log.debug to all silent exception handlers in ssh_client

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

gui/tabs/terminal_tab.py

@@ -142,9 +142,8 @@ class TerminalTab(ctk.CTkFrame):
         session = self._session  # local ref for thread safety
         if session and session.connected:
             session.send(data)
-        elif self._current_alias and not self._intentional_disconnect:
-            # Session dead — trigger reconnect
-            self._reconnect_count = 0
+        elif self._current_alias and not self._intentional_disconnect and self._reconnect_count == 0:
+            # Session dead, no reconnect in progress — trigger one attempt
             self._on_disconnected()
 
     def _on_resize(self, cols: int, rows: int):