Fix raw ANSI codes displaying for CompletionError in prompt_toolkit

When raising a CompletionError with apply_style=True during tab completion
in prompt_toolkit mode, the error message was printed directly to stdout using
ANSI codes. prompt_toolkit's patch_stdout would capture this but fail to
interpret the ANSI codes, resulting in raw escape sequences being displayed.

This commit fixes the issue by:
1.  Modifying cmd2.complete to capture the styled error message into
    self.completion_header instead of printing directly to stdout.
2.  Updating Cmd2Completer.get_completions (in pt_utils.py) to print
    completion_header using print_formatted_text wrapped in ANSI,
    which correctly renders the styled text above the prompt.
3.  Updating tests/conftest.py complete_tester to print completion_header
    so existing tests (like test_completion_error) continue to pass by
    capturing the error output.

Author: tleonhardt

cmd2/cmd2.py

@@ -1624,6 +1624,7 @@ def _reset_completion_defaults(self) -> None:
         self.formatted_completions = ''
         self.completion_matches = []
         self.display_matches = []
+        self.completion_header = ''
         self.matches_delimited = False
         self.matches_sorted = False
 
@@ -2468,11 +2469,12 @@ def complete(
                 # If apply_style is True, then this is an error message that should be printed
                 # above the prompt so it remains in the scrollback.
                 if ex.apply_style:
-                    self.print_to(
-                        sys.stdout,
-                        "\n" + err_str,
-                        style=Cmd2Style.ERROR,
-                    )
+                    # Render the error with style to a string using Rich
+                    console = ru.Cmd2GeneralConsole()
+                    with console.capture() as capture:
+                        console.print("\n" + err_str, style=Cmd2Style.ERROR)
+                    self.completion_header = capture.get()
+
                 # Otherwise, this is a hint that should be displayed below the prompt.
                 else:
                     self.completion_hint = err_str

cmd2/pt_utils.py

@@ -76,6 +76,11 @@ def get_completions(self, document: Document, _complete_event: object) -> Iterab
             print_formatted_text(ANSI("\n" + self.cmd_app.formatted_completions))
             self.cmd_app.formatted_completions = ""
 
+        # Print completion header (e.g. CompletionError) if present
+        if self.cmd_app.completion_header:
+            print_formatted_text(ANSI(self.cmd_app.completion_header))
+            self.cmd_app.completion_header = ""
+
         # Print hint if present
         if self.cmd_app.completion_hint:
             print_formatted_text(ANSI(self.cmd_app.completion_hint))

tests/conftest.py

@@ -151,6 +151,11 @@ def get_endidx() -> int:
     if app.completion_hint:
         print(app.completion_hint)
 
+    # If the completion resulted in a header being set (e.g. CompletionError), then print it now
+    # so that it can be captured by tests using capsys.
+    if app.completion_header:
+        print(app.completion_header)
+
     return res