ctdl-validate 0.2.1

Fixes a version-reporting defect in v0.2.0: the package hard-coded
__version__ = "0.1.0" while built as 0.2.0, so --version, the JSON report
stamp and the fetch User-Agent all announced the wrong release.

__version__ now derives from installed distribution metadata, guarded by an
AST test that fails if any module reintroduces a version literal.

ctdl-validate 0.2.0

Composite GitHub Action for CTDL JSON-LD structural validation, so a consumer
can pin a tag that contains it.

Also fixes the sync gate, which ran only `uv sync --frozen` and therefore
could not fail on lockfile drift (CQ-09).

Verified at this tag: 179 tests, 94.83% coverage, ruff, mypy strict, pip-audit.