Support prompt format strings for dynamic terminal titles

[rolandwalker]

Description

• tab title
• window title
• tmux window title (other multiplexers could be supported)
• tmux pane title (other multiplexers could be supported)

Motivation: power users often have multiple connections open. We should help users keep track.

Tmux window-title example, showing the schema name:

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

Findings

1. Potential crash when $TMUX is set but tmux is unavailable

   • File: mycli/main.py:1597
   • subprocess.run(['tmux', 'rename-window', title], ...) is not wrapped in try/except. If tmux is not on PATH (or unavailable in minimal/container envs), this raises FileNotFoundError and can crash interactive startup / \u flow.
   • Action: guard with shutil.which("tmux") and/or catch OSError around the call.

2. Terminal escape injection risk in title sequences

   • Files: mycli/main.py:1574, mycli/main.py:1585, mycli/main.py:1614
   • Title text is inserted directly into OSC sequences after only strip_ansi(...). Control characters like BEL (\x07) or ST/ESC variants are not explicitly removed, so hostile prompt-derived values (e.g., schema/user/host content) could prematurely terminate OSC and inject terminal controls.
   • Action: sanitize title strings by removing all C0/C1 control chars (at minimum \x00-\x1F, \x7F, and ESC-related terminators) before printing OSC.

3. Missing regression tests for new title code paths

   • Current PR only updates config fixture text (test/myclirc); no behavioral tests for the new helpers.
   • Action: add tests for:
     • no crash when $TMUX is set but tmux executable is missing,
     • control-character sanitization in generated titles,
     • set_all_external_titles() invocation points (initial prompt + \u database switch).