GeezerVison

why: libtmux 0.59.0 adds tmux 3.7 support and works around an upstream
tmux 3.7 regression where break-pane crashed the server with a
NULL-pointer dereference. Picking it up lets tmuxp run on tmux 3.7.

what:
- Bump libtmux ~=0.58.1 -> ~=0.59.0 in pyproject.toml
- Update uv.lock to libtmux 0.59.0 from PyPI

libtmux 0.59.0 (2026-06-27):
- Add tmux 3.7 to the tested version matrix (3.2a-3.7)
- Fix: Pane.break_pane no longer crashes the tmux 3.7 server (#693)

Release: https://github.com/tmux-python/libtmux/releases/tag/v0.59.0
Changelog: https://libtmux.git-pull.com/history.html#libtmux-0-59-0-2026-06-27

why: tmux 3.7 reworded the pane-overflow error from "no space for new
pane" to "size or position no space for a new pane". The issue-800
regression test pinned the old text and failed on tmux 3.7.

what:
- Widen the pytest.raises match to r"no space for (a )?new pane" so it
  matches both the pre-3.7 and 3.7 phrasings
- Add a comment documenting the tmux 3.7 wording change

why: libtmux 0.59.0 adds tmux 3.7 support, so tmuxp should verify it
builds and tests cleanly against the new release.

what:
- Add '3.7' to the tmux-version build matrix alongside 3.2a-3.6 and
  master in .github/workflows/tests.yml

why: Record the libtmux floor bump and tmux 3.7 support under the
1.71.0 unreleased block. The release lead paragraph and version
header are added by the maintainer at tag time, not by this PR.

what:
- Record the libtmux ~=0.58.1 -> ~=0.59.0 floor bump under Dependencies
- Note tmux 3.7 support under What's new, scoped to the user-visible
  change (supported version range) without CI, break-pane, or test
  mechanics