Replace create-pull-request action with gh CLI in release workflow

[Copilot]

The create-release.yml workflow was using peter-evans/create-pull-request@v6 after manually creating, committing, and pushing a branch. This action expects to handle the entire commit/push/PR lifecycle itself, not work with pre-pushed branches.

Changes:

• Replaced create-pull-request action with gh pr create CLI command
• Extracted PR body into a bash variable to handle multi-line strings cleanly

Before:

- name: Create release branch
  run: |
    git checkout -b $BRANCH_NAME
    git commit -am "chore: Bump version to ${{ env.new_version }}"
    git push origin $BRANCH_NAME

- name: Create Pull Request
  uses: peter-evans/create-pull-request@v6
  with:
    branch: release/${{ env.new_version }}
    # ... attempts to work with already-pushed branch

After:

- name: Create release branch
  run: |
    git checkout -b $BRANCH_NAME
    git commit -am "chore: Bump version to ${{ env.new_version }}"
    git push origin $BRANCH_NAME

- name: Create Pull Request
  run: |
    gh pr create \
      --base main \
      --head release/${{ env.new_version }} \
      --body "$PR_BODY"

This aligns with the standard pattern: when manually managing branch creation and pushing, use gh pr create or the REST API rather than workflow actions designed for the full lifecycle.

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[mkistler]

I'm going to start over on this.