Add v0.1.3 release notes and include them in release workflow; update README and tests

[liyown]

Motivation

• Prepare and publish the v0.1.3 release with human-readable release notes and ensure the release automation uses them.
• Keep the docs and install instructions in README.md aligned with the new release version and make the prepared notes discoverable.
• Ensure packaging/release automation changes are validated by tests.

Description

• Add release notes file at .github/releases/v0.1.3.md containing highlights and install instructions for v0.1.3.
• Update the release workflow in .github/workflows/release.yml to check out the repository and pass body_path: .github/releases/${{ env.RELEASE_VERSION }}.md to the GitHub release action so release notes are used as the release body.
• Update README.md to reference v0.1.3 in the install command and tag example and to mention the prepared release notes location.
• Update release_packaging_test.go to assert the new workflow steps and body_path usage are present in the release workflow.

Testing

• Ran the updated packaging test release_packaging_test.go via go test ./... and the test suite completed successfully.
• The test confirms the release workflow contains Checkout release notes and body_path: .github/releases/${{ env.RELEASE_VERSION }}.md and the README references the v0.1.3 artifacts.

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Codex Task