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>

gui/sidebar.py

@@ -29,6 +29,8 @@ class Sidebar(ctk.CTkFrame):
         self.search_var.trace_add("write", lambda *_: self._refresh_list())
         self.search_entry = ctk.CTkEntry(self, placeholder_text=t("search"), textvariable=self.search_var)
         self.search_entry.pack(fill="x", padx=10, pady=(5, 10))
+        # Enable undo functionality
+        self.search_entry._entry.config(undo=True)
 
         # Server list
         self.list_frame = ctk.CTkScrollableFrame(self, fg_color="transparent")