Fixes#2492.
`generate_systemd_unit()` and `get_python_path()` hardcoded `venv`
as the virtualenv directory name. When the virtualenv is `.venv`
(which `setup-hermes.sh` and `.gitignore` both reference), the
generated systemd unit had incorrect VIRTUAL_ENV and PATH variables.
Introduce `_detect_venv_dir()` which:
1. Checks `sys.prefix` vs `sys.base_prefix` to detect the active venv
2. Falls back to probing `.venv` then `venv` under PROJECT_ROOT
Both `get_python_path()` and `generate_systemd_unit()` now use
this detection instead of hardcoded paths.
Co-authored-by: Hermes <hermes@nousresearch.ai>
ce39f9cc44