ci: add GitHub Actions release pipeline

[johncburns1]

Summary

• add reusable GitHub Actions CI for lint, format check, mypy, pytest, and build
• add a version policy gate that checks feature branches against main and checks main against the latest semver tag
• add an automated GitHub Release flow for main that uploads built artifacts without any PyPI publish step

Details

• introduces .github/scripts/version_policy.py and focused unit coverage in .github/tests/test_version_policy.py
• keeps the release surface repo-specific by deriving shipped package paths from pyproject.toml
• avoids the tag-before-release rerun wedge from the SDK MR by creating or updating the GitHub Release directly from the workflow
• uses uv sync --group dev --locked in CI to keep workflow installs pinned to uv.lock

Verification

• uv run pytest .github/tests/test_version_policy.py -q
• uv run ruff check .
• uv run ruff format --check .
• uv run mypy dispatch_cli
• uv run pytest --cov=dispatch_cli --cov-report=term-missing tests .github/tests/test_version_policy.py
• uv build