Add ruff support to Taskfile and fix the smoketest failure for cli

[rafaelherik]

This PR brings two small but important improvements:

1. Add Ruff support to Taskfile
   * Introduces a new run-check task in Taskfile.yml that runs poetry run ruff check .
   * Allows us to lint the full codebase with Ruff via task run-check

2. Clean up task artifacts

   • Updates .gitignore to ignore the entire .task/ directory
     * Removes the now-untracked checksum file at .task/checksum/install

3. Fix CLI smoke test failure
   * Adjusts imports in tests/test_cli.py (splits import subprocess, sys, json into separate imports)
   * Resolves a test failure caused by an unused/malformed import

[bcdady]

• Resolves a test failure caused by an unused/malformed import

Oops, sorry about that one.