Show the plugin version in summary.txt

fill_resistance.__version__ is the runtime source (metadata.json and
pyproject.toml are excluded from deployment); a test pins all three
to the same number.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_version.py

@@ -0,0 +1,33 @@
+"""fill_resistance.__version__ is the runtime source of the version:
+it must match the packaging metadata (which is not deployed with the
+plugin) and show up in summary.txt."""
+import json
+import re
+from pathlib import Path
+
+import fill_resistance
+from fill_resistance import raster, report, solver
+from tests.util import NM, strip_problem
+
+ROOT = Path(__file__).resolve().parent.parent
+
+
+def test_version_matches_packaging_metadata():
+    meta = json.loads((ROOT / "metadata.json").read_text(encoding="utf-8"))
+    assert meta["versions"][0]["version"] == fill_resistance.__version__
+
+    pyproject = (ROOT / "pyproject.toml").read_text(encoding="utf-8")
+    m = re.search(r'^version = "([^"]+)"', pyproject, re.M)
+    assert m is not None
+    assert m.group(1) == fill_resistance.__version__
+
+
+def test_summary_shows_version(tmp_path):
+    problem = strip_problem()
+    stack = raster.rasterize_stack(problem, 1.0 * NM)
+    e1, e2 = raster.electrode_masks(stack, problem)
+    result = solver.run_solve(problem, stack, e1, e2, 1.0,
+                              contact_model="equipotential")
+    text = report.write_summary(tmp_path, problem, stack,
+                                result).read_text(encoding="utf-8")
+    assert fill_resistance.__version__ in text.splitlines()[0]