feat: modernize project with uv, add pytest test suite

- Add pyproject.toml with modern Python packaging (PEP 517/518)
- Add uv-based dependency management replacing inline venv bootstrap
- Add requirements.txt and requirements-dev.txt for compatibility
- Add mise.toml with dev tasks (test, lint, run, sync, ci)
- Add .python-version pinned to Python 3.12
- Add comprehensive pytest test suite (73 tests) for:
  - engine/config, filter, terminal, sources, mic, ntfy modules
- Configure pytest with coverage reporting (16% total, 100% on tested modules)
- Configure ruff for linting with Python 3.10+ target
- Remove redundant venv bootstrap code from mainline.py
- Update .gitignore for uv/venv artifacts

Run 'uv sync' to install dependencies, 'uv run pytest' to test.

.gitignore

@@ -1,5 +1,11 @@
 __pycache__/
 *.pyc
 .mainline_venv/
+.venv/
+uv.lock
 .mainline_cache_*.json
 .DS_Store
+htmlcov/
+.coverage
+.pytest_cache/
+*.egg-info/