Adds scripts/decisions_lib.py, the shared parser for ErsatzTV decision
records (docs/decisions.md + docs/decisions/*.md). Parses H2 sections
into Record dataclasses, distinguishing migrated records (visible
metadata block: key/status/since/supersedes/superseded-by + Rule/
Signals/Mechanics) from legacy-unmigrated ones with no metadata line.
scripts/ is now an importable package (scripts/__init__.py,
scripts/tests/__init__.py) so later tools can `import scripts.decisions_lib`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
