feat: support uv-managed Python Actors in apify create

[vdusek]

apify create hard-coded pip install -r requirements.txt for Python Actors, so creating a uv-managed template — which ships pyproject.toml + uv.lock and no requirements.txt — failed during dependency install with Could not open requirements file.

create now detects uv-managed Python/Scrapy projects by the presence of a committed uv.lock and installs their dependencies with uv sync instead. The check runs before the system-Python detection, since uv provides the interpreter pinned in .python-version itself, and falls back to a warning with install instructions when the uv executable isn't found.

This unblocks the upcoming python-uv template (apify/actor-templates#800).