Add example embedding a cmd2 app in a Textual app with textual-tty

[DG-Elom]

Adds examples/textual_tty_embed.py, showing how to embed a cmd2 app in a Textual app with textual-tty, with a realtime status panel next to the terminal.

• The Textual app runs the cmd2 app (this same script with --cmd2-only) in a textual-tty Terminal, so the cmd2 app is a plain prompt-toolkit app that doesn't know it's embedded.
• The cmd2 app reports its state (idle/running, commands run, last command and duration) with set_window_title() from precmd / command finalization hooks. The Terminal.TitleChanged message updates the panel, so no extra IPC is needed. A Textual-driven clock panel updates independently.
• textual and textual-tty are not cmd2 dependencies. The module docstring shows how to run it: uv run --with textual-tty examples/textual_tty_embed.py.
• Added to examples/README.md.

Tested headless with Textual's Pilot (textual 8.2.8, textual-tty 0.4.0, Linux): typing commands into the embedded terminal shows cmd2's output, and the status panel goes idle -> running -> idle with the command count updated. make test, make mypy, make docs-test and the prek hooks pass.

Note that textual-tty is still pre-alpha, so the example may need small updates if its API changes. Happy to adjust the approach (e.g. a socket instead of the window title) if you prefer.

Closes #1771

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.75%. Comparing base (93cfe81) to head (a35a055).

Additional details and impacted files

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  Misses         16       16           

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[kmvanbrunt]

Thanks for making this example. It works quite well, but I did run into one issue.

After running enough commands where the prompt should display at the bottom of the screen, it instead is hidden outside the CLI panel.

[DG-Elom]

Thanks for catching this, I can reproduce it. The Terminal widget sizes its pseudo-terminal from its outer size, border included. With border: round on the Terminal itself, the PTY was 2 rows (and 2 columns) bigger than the visible area, so once the screen filled up prompt-toolkit drew the prompt on a row that was clipped. In a headless run at 100x30 the visible area was 26 rows, the PTY was 28, and the cursor ended on row 27.

I moved the border to a wrapping container in a35a055, so the PTY now matches the visible area (26 rows, cursor on row 25 after 40 commands).