Use release-please body output instead of CHANGELOG.md in release workflow

[Copilot]

The release workflow was referencing the entire CHANGELOG.md file for GitHub release bodies, making releases verbose with all historical changes instead of version-specific notes.

Changes

• Added body output from release-please step to bump job outputs
• Changed GitHub Release step to use body parameter instead of body_path: CHANGELOG.md
• Removed generate_release_notes: true (redundant with release-please body)

  outputs:
    release_created: ${{ steps.release.outputs.release_created }}
    tag_name: ${{ steps.release.outputs.tag_name }}
+   body: ${{ steps.release.outputs.body }}

  - name: GitHub Release
    uses: softprops/action-gh-release@v2
    with:
      tag_name: ${{ needs.bump.outputs.tag_name }}
-     generate_release_notes: true
-     body_path: CHANGELOG.md
+     body: ${{ needs.bump.outputs.body }}
      prerelease: ${{ github.event.inputs.release-type == 'next' }}

Releases now contain only the relevant version's notes as generated by release-please.

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