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/test_cli.py

@@ -1,19 +1,23 @@
 import subprocess
 import sys
 
+import pytest
 
+
+@pytest.mark.unit
 def test_version_subcommand():
     r = subprocess.run(
-        [sys.executable, "-m", "invisible-playwright", "version"],
+        [sys.executable, "-m", "invisible_playwright", "version"],
         capture_output=True, text=True, check=True,
     )
     assert "firefox-" in r.stdout
-    assert "invisible-playwright" in r.stdout.lower()
+    assert "invisible_playwright" in r.stdout.lower()
 
 
+@pytest.mark.unit
 def test_help_subcommand():
     r = subprocess.run(
-        [sys.executable, "-m", "invisible-playwright", "--help"],
+        [sys.executable, "-m", "invisible_playwright", "--help"],
         capture_output=True, text=True,
     )
     assert r.returncode == 0