Add automatic PyPI updates

[NiceDayZc]

What changed

• checks the official PyPI JSON endpoint in the background when the TUI starts
• installs newer vantadsp releases with the same Python interpreter and reports restart status in Activity
• protects editable development checkouts from automatic replacement
• adds vantactl check-update and vantactl update
• converts offline/network failures into explicit status results instead of tracebacks
• uses a fixed package name and argument-list subprocess invocation

Validation

• 59 tests passed
• full-package branch coverage: 70.98%
• Ruff, formatting, and mypy passed
• Bandit passed
• pip-audit found no known vulnerabilities
• live PyPI check correctly reports local 0.2.2 ahead of published 0.2.1
• wheel/sdist build and Twine checks passed