ci: restore matrix testing and tagged PyPI releases

[SergeiNikolenko]

Restores the reverted CI/CD and packaging changes from #45 on top of current main.

What changed:

• restores GitHub Actions CI, manual PyPI publish, and tag-only release workflows
• keeps release publication on version tags only
• removes unused hydra-core from package metadata
• aligns package license metadata with the repository license
• updates CI to run stable checks for the current codebase
• fixes stale CLI reproducibility tests to match the current run_matcha API
• applies LiTr-style Ruff configuration structure with pragmatic ignores to reduce noise

Local verification:

• uv run --with ruff ruff check tests
• uv run pytest -o addopts= tests -q
• uv build
• uvx twine check dist/*