uv dev environment, README writing pass, publish hygiene

- pyproject.toml + uv.lock: uv-managed dev environment (uv sync /
  uv run pytest). requirements.txt stays: KiCad builds the plugin's
  runtime venv from it and the PCM zip packages it.
- README: em-dash and run-on cleanup (34 -> 22, the rest deliberate),
  split the 120-word THT solder-joint sentence, fix the documented
  ADAPTIVE_MAX_CELL_UM value (2 mm -> 1 mm, config has 1000 um), fix
  the *Packaging / publishing* cross-reference, dev sections now use
  uv sync / uv run.
- LLM disclaimer: "most commits" carry the trailer (32 of 39), figures
  claim now excepts the hand-drawn hole cross-section, reference the
  UT3513+ measured-vs-computed validation.
- .gitignore: local AI-tooling artifacts; deploy scripts exclude
  pyproject.toml/uv.lock; error-figure title punctuation aligned with
  the other window titles.

pyproject.toml

@@ -0,0 +1,28 @@
+# Development environment only (uv sync / uv run). The KiCad plugin
+# manager builds the runtime venv itself from requirements.txt — keep
+# the dependency list there in sync with [project.dependencies].
+[project]
+name = "fill-resistance"
+version = "1.1.0"
+description = "DC/AC resistance of copper zone fills and traces between two contacts (KiCad 10 plugin)"
+license = "GPL-3.0-or-later"
+requires-python = ">=3.11"
+dependencies = [
+    "kicad-python>=0.7.0",
+    "numpy",
+    "scipy",
+    "pyamg",
+    "matplotlib",
+    "PySide6",
+]
+
+[dependency-groups]
+dev = [
+    "pytest",
+]
+
+[tool.uv]
+package = false
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]