[BUG] Crash on autocompletion

[AlAtsal]

Crash on autocompletion: AttributeError: 'list' object has no attribute 'to_strings'

Describe the bug

When attempting to trigger autocompletion (by pressing TAB twice) in the CLI, the application crashes with an AttributeError.

Traceback

╭─────────────────────────────── Traceback (most recent call last) ────────────────────────────────╮
  │ /home/aatsalak/repos/quads-client/venv/lib64/python3.14/site-packages/cmd2/cmd2.py:2683 in        │
  │ complete                                                                                         │
  │                                                                                                  │
  │   2680 │   │   │   │   )                                                                             │
  │   2681 │   │   │   │   custom_settings = utils.CustomCompletionSettings(parser)                      │
  │   2682 │   │   │   │                                                                                 │
  │ ❱ 2683 │   │   │   │   completions = self._perform_completion(text, line, begidx, endidx,            │
  │        custom_settings)                                                                          │
  │   2684 │   │   │   │                                                                                 │
  │   2685 │   │   │   │   # Check if we need to restore a shortcut in the completion text                │
  │   2686 │   │   │   │   # so it doesn't get erased from the command line.                             │
  │                                                                                                  │
  │ /home/aatsalak/repos/quads-client/venv/lib64/python3.14/site-packages/cmd2/cmd2.py:2609 in        │
  │ _perform_completion                                                                              │
  │                                                                                                  │
  │   2606 │   │                                                                                     │
  │   2607 │   │   # Check if we need to add an opening quote                                        │
  │   2608 │   │   if not completion_token_quote:                                                    │
  │ ❱ 2609 │   │   │   matches = completions.to_strings()                                            │
  │   2610 │   │   │                                                                                     │
  │   2611 │   │   │   if any(" " in match for match in matches):                                        │
  │   2612 │   │   │   │   _add_opening_quote = True                                                     │
  ╰──────────────────────────────────────────────────────────────────────────────────────────────────╯
  AttributeError: 'list' object has no attribute 'to_strings'

Root Cause

This is caused by changes introduced in the cmd2 4.x completion API. The complete_* methods must now return cmd2.CompletionItem objects (which have .to_strings() method) instead of plain lists.