fix: __version__ comes from package metadata; add --version flag (#24)

Two bugs reported in #24:

1. `python -m invisible_playwright version` printed the literal "0.1.0"
   regardless of the installed version. Root cause: __version__ in
   __init__.py was hardcoded and never bumped when the package version
   moved past 0.1.0. Fix: read from importlib.metadata so __version__
   stays in lockstep with pyproject.toml's `version` field by construction.

2. `python -m invisible_playwright --version` errored with "the
   following arguments are required: cmd". Root cause: the parser had
   `required=True` on its subparsers and no top-level --version flag.
   Fix: add a top-level `--version`/`-V` flag using argparse's standard
   version action, drop `required=True`, and reroute the "no subcommand"
   case through parser.error() so the existing test_no_subcommand_errors
   contract is preserved.

7 new unit tests pin both behaviours so they can't regress silently.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_version.py

@@ -0,0 +1,103 @@
+"""Regression tests for issue #24: CLI version reporting.
+
+Two distinct symptoms reported by `i43-j`:
+  1. `python -m invisible_playwright --version` errored out (only the
+     `version` subcommand worked).
+  2. `python -m invisible_playwright version` printed the literal string
+     "0.1.0" regardless of the installed version (a stale hardcoded
+     `__version__` in __init__.py that nobody had remembered to bump).
+
+These tests pin down both behaviours so the regressions don't sneak back
+in via a future copy/paste.
+"""
+import io
+import re
+import subprocess
+import sys
+from contextlib import redirect_stdout
+
+import pytest
+
+import invisible_playwright
+from invisible_playwright import __version__, cli
+
+
+pytestmark = pytest.mark.unit
+
+
+def test_version_matches_installed_package_metadata():
+    """__version__ must come from importlib.metadata, not a hardcoded literal,
+    so it can never drift from the pyproject.toml `version` field."""
+    from importlib.metadata import version as pkg_version
+    assert __version__ == pkg_version("invisible-playwright")
+
+
+def test_version_is_not_the_stale_010_string():
+    """Issue #24 regression: __version__ used to be hardcoded as '0.1.0'
+    and never updated. If this ever returns to a literal '0.1.0' the
+    package has been published or shipped with stale metadata."""
+    assert __version__ != "0.1.0", (
+        "__version__ is the stale hardcoded '0.1.0' string — issue #24 has "
+        "regressed. Use importlib.metadata to derive it from pyproject.toml."
+    )
+
+
+def test_version_subcommand_prints_real_version():
+    """`invisible-playwright version` must print the actual installed version,
+    not the old hardcoded '0.1.0'."""
+    buf = io.StringIO()
+    with redirect_stdout(buf):
+        rc = cli.main(["version"])
+    assert rc == 0
+    out = buf.getvalue()
+    assert f"invisible_playwright {__version__}" in out
+    assert "0.1.0" not in out or __version__ == "0.1.0"  # safety: only allowed if truly 0.1.0
+    assert "BINARY_VERSION=" in out
+    assert "Firefox " in out
+
+
+def test_dash_dash_version_flag_works():
+    """Issue #24 reporter: `python -m invisible_playwright --version` used to
+    error with 'the following arguments are required: cmd' because there was
+    no top-level --version flag, only the `version` subcommand. Now the
+    Python convention works too."""
+    # argparse's --version action calls sys.exit(0) directly, so use subprocess.
+    r = subprocess.run(
+        [sys.executable, "-m", "invisible_playwright", "--version"],
+        capture_output=True, text=True, timeout=15,
+    )
+    assert r.returncode == 0, f"--version returned {r.returncode}, stderr={r.stderr!r}"
+    # argparse may emit on stdout or stderr depending on version
+    combined = r.stdout + r.stderr
+    assert "invisible_playwright" in combined
+    assert __version__ in combined
+
+
+def test_no_args_prints_help_not_traceback():
+    """`python -m invisible_playwright` with no args should be graceful
+    (print help, exit non-zero) rather than crashing with a traceback."""
+    r = subprocess.run(
+        [sys.executable, "-m", "invisible_playwright"],
+        capture_output=True, text=True, timeout=15,
+    )
+    # Either prints help (rc=2) or shows usage. Must NOT contain a traceback.
+    assert "Traceback" not in (r.stdout + r.stderr)
+    assert "usage:" in (r.stdout + r.stderr).lower()
+
+
+def test_dash_V_short_flag_works():
+    """Alias `-V` for `--version` (Python convention)."""
+    r = subprocess.run(
+        [sys.executable, "-m", "invisible_playwright", "-V"],
+        capture_output=True, text=True, timeout=15,
+    )
+    assert r.returncode == 0
+    assert __version__ in (r.stdout + r.stderr)
+
+
+def test_version_matches_semver_shape():
+    """Sanity: version should look like a semver (digits.digits.digits)
+    or a PEP-440 dev marker, not a placeholder string."""
+    assert re.match(r"^\d+\.\d+\.\d+", __version__), (
+        f"__version__ {__version__!r} doesn't look like a real version"
+    )