chore: remove stale validate_coverage.py; decide whether mypy gates CI #157

Two dev-tooling leftovers that no longer match how the repo works.

1. src/utils/validate_coverage.py is stale and crashes

• Stale: it expects test files the repo no longer has (test_tools_modeling.py, test_adapters.py and others). Tests now mirror src/, and tests/integration/test_test_layout.py enforces that.
• Crashes: on Windows it fails at startup: printing an emoji raises UnicodeEncodeError with the default cp1252 console encoding.
• Unused: nothing references it, not CI, not dev-commands.ps1, not the docs.

Proposed: delete it. Coverage is already enforced by pytest-cov (100%) and the layout by test_test_layout.py. If anything in it is still wanted, move that into those.

2. mypy is configured but not enforced

pyproject.toml and dev-commands.ps1 configure mypy, but CI doesn't run it. It reports errors on main: 40 in adapters/solidworks/documentation.py alone. Most are lambdas passed to _attempt ("Cannot infer type of lambda") and Any returns. New code adds more of the same, and nobody notices.

Proposed: decide whether mypy should gate:

• If yes: fix the existing errors module by module. Typing _attempt generically (def _attempt[T](self, op: Callable[[], T], default: T) -> T) should clear most of them. Then add a CI step.
• If no: remove the mypy config, so editors stop flagging errors nobody will fix.

Acceptance

• validate_coverage.py is removed, or rewritten so it runs and matches the current layout.
• mypy either gates in CI with zero errors, or is removed from the config.