When Poetry is configured with virtualenvs.in-project = true,
poetry env info --path returns "." instead of the full path.
This causes the plugin to fail with "no such file or directory: ./bin/activate".
Changes:
- Handle case where poetry returns "." by converting to $PWD/.venv
- Add safety check to ensure activate script exists before sourcing
- Maintain backward compatibility with existing setups
Fixes issue with in-project virtual environments used in monorepos and git worktrees.
