test: add pytest markers, conftest, fix Windows-incompatible existing tests

- Add tests/conftest.py with deterministic_rng + sample_profile fixtures
- Register unit/integration/e2e markers in pyproject.toml
- Mark existing 14 tests as @pytest.mark.unit
- Fix test_cli.py: use 'invisible_playwright' (underscore) for 'python -m'
- Fix test_translate_includes_gpu_renderer: assert Windows behavior (empty renderer)

tests/conftest.py

@@ -0,0 +1,17 @@
+import random
+
+import pytest
+
+from invisible_playwright._fpforge import generate_profile
+
+
+@pytest.fixture
+def deterministic_rng():
+    """Seeded RNG for reproducible tests."""
+    return random.Random(42)
+
+
+@pytest.fixture
+def sample_profile():
+    """A Profile generated from seed=42 for reuse across tests."""
+    return generate_profile(seed=42)