Accept Python 3.14+ in venv provisioning (use a >=3.9 floor)

[tedvask]

pick_python() in postinstall.sh and voxd.wrapper enumerated supported
interpreters (3.9|3.10|3.11|3.12|3.13). On distros that ship Python 3.14
as the system interpreter (Fedora 43+), nothing is accepted: python3
resolves to 3.14 (rejected) and no 3.9–3.12 binary exists. Install then
fails to create /opt/voxd/.venv, and voxd exits with "System Python
3.14 is unsupported and no newer Python was found" — even though
main.py already states the contract as "3.9+".

This replaces the enumerated allowlist with a numeric >= 3.9 comparison
and adds python3.14/3.13 to the probe order, so current and future
releases are accepted automatically. All runtime deps already ship
3.14-compatible wheels (numpy/psutil/pyyaml cp314, PyQt6 abi3,
sounddevice/pyqtgraph pure-Python), so the venv builds cleanly on 3.14.

The wrapper's guard case is intentionally left unchanged so 3.14 routes
into venv provisioning (deps guaranteed) rather than direct exec.