v1.2.0

First PyPI publish. Continues the existing v1.0.0 -> v1.1.0 git tag line (see CHANGELOG.md and DECISIONS D74 for why the first PyPI version is 1.2.0, not 1.0.0). All backward-compatible additions since v1.1.0. This release was produced via the repo's own release-review Section 9 (run 20260712-173338): full suite green (215 passed), CI green across the 3-OS x 2-Python matrix, gitleaks clean, twine check passed.