Migrate from pip/pip-tools to uv

[Simrayz]

We're already using uv in other projects. Migrating Argus would give us:

• Much faster CI (tox env creation + dep install across 4 matrix jobs)
• Faster local tox runs and upgrade-deps
• Faster Docker builds
• Less CI config (setup-uv handles caching, no more manual actions/cache)

The migration is low-risk since uv pip compile and tox-uv are drop-in replacements. Lock file format stays the same, pyproject.toml doesn't change.