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.

mainline.py

@@ -5,40 +5,7 @@ Digital news consciousness stream.
 Matrix aesthetic · THX-1138 hue.
 """
 
-import subprocess, sys, pathlib
-
-# ─── BOOTSTRAP VENV ───────────────────────────────────────
-_VENV = pathlib.Path(__file__).resolve().parent / ".mainline_venv"
-_MARKER = _VENV / ".installed_v3"
-
-def _ensure_venv():
-    """Create a local venv and install deps if needed."""
-    if _MARKER.exists():
-        return
-    import venv
-    print("\033[2;38;5;34m  > first run — creating environment...\033[0m")
-    venv.create(str(_VENV), with_pip=True, clear=True)
-    pip = str(_VENV / "bin" / "pip")
-    subprocess.check_call(
-        [pip, "install", "feedparser", "Pillow", "-q"],
-        stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
-    )
-    _MARKER.touch()
-
-_ensure_venv()
-
-# Install sounddevice on first run after v3
-_MARKER_SD = _VENV / ".installed_sd"
-if not _MARKER_SD.exists():
-    _pip = str(_VENV / "bin" / "pip")
-    subprocess.check_call([_pip, "install", "sounddevice", "numpy", "-q"],
-                          stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
-    _MARKER_SD.touch()
-
-sys.path.insert(0, str(next((_VENV / "lib").glob("python*/site-packages"))))
-
-# ─── DELEGATE TO ENGINE ───────────────────────────────────
-from engine.app import main  # noqa: E402
+from engine.app import main
 
 if __name__ == "__main__":
     main()