fix: editable alias in server dialog + Ctrl+Z undo for all input fields

- Alias field no longer disabled when editing server profile
- Duplicate alias check on rename, session pool migration
- Enable undo (Ctrl+Z) on all CTkEntry widgets across the project

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

core/session_pool.py

@@ -214,6 +214,17 @@ class SessionPool:
         """Clean up sessions when a server is deleted."""
         self.disconnect_session(alias)
 
+    def rename_server(self, old_alias: str, new_alias: str):
+        """Rename a server's session references (after alias change)."""
+        with self._lock:
+            if old_alias in self._sessions:
+                session_data = self._sessions.pop(old_alias)
+                session_data.alias = new_alias
+                self._sessions[new_alias] = session_data
+            if old_alias in self._last_used_order:
+                ts = self._last_used_order.pop(old_alias)
+                self._last_used_order[new_alias] = ts
+
     def get_active_sessions(self) -> list:
         """Get list of aliases for active sessions."""
         with self._lock: