v0.1.1

The two issues from the first use in another repository, plus housekeeping after the
release.

• Record the v0.1.0 DOIs (concept 10.5281/zenodo.22649033, version 10.5281/zenodo.22649034) and add the PyPI, CI and DOI badges.
• CI passes CODECOV_TOKEN and fails the upload loudly: five runs had uploaded nothing while green.
• Coverage measures the CLI and every subprocess (the parallel + patch=subprocess modes);
  in-process CLI tests and the remaining core branches take it from 72 % to 100 %.
• A relative --python (or PYTHON) passed the existence check, then crashed with a
  traceback from the sandbox (#1): the check ran in the caller's cwd, pytest in the
  sandbox. The interpreter is now made absolute once, before the run: --python relative
  to the caller's cwd, a declaration's PYTHON relative to the root like ROOT and
  PATHS (a bare name is still looked up on PATH).
• test_run_verbose_only_keep_and_stop no longer leaves a sandbox in $TMPDIR on every
  suite run (14 per self-check), and now asserts the kept directory exists (#2).
• Three new self-contracts pin the fixes (python-unresolved, keep-ignored,
  declared-python-cwd-anchored); the self-check reads 16 OK.