release: rename package to jsondiffview and prepare 1.0.0

[WAcry]

Summary

• rename the published CLI to jsondiffview and switch to a flat src/ layout
• add release-facing docs and packaging metadata for the 1.0.0 release
• add GitHub Actions CI and trusted-publishing release workflows

Verification

• python -m pytest -q
• uv run pytest
• uv build --no-sources
• uvx twine check dist/jsondiffview-1.0.0.tar.gz dist/jsondiffview-1.0.0-py3-none-any.whl
• install the built wheel and run jsondiffview --help, jsondiffview --version, and a changed-view smoke test