ci: remove auto-merge to fix release triggering (#479)

GitHub's auto-merge feature uses an internal token that cannot trigger
workflows. Even with manual approval, the merge performed by auto-merge
doesn't trigger the release workflow.

Removing auto-merge means:
1. Version PR is created with CI running
2. User manually merges the PR (clicking "Merge")
3. The merge triggers the release workflow
4. Package is published

This aligns with industry standard practice for changesets.

Author: TabishB

.github/workflows/release-prepare.yml

@@ -47,7 +47,6 @@ jobs:
 
       # Opens/updates the Version Packages PR; publishes when the Version PR merges
       - name: Create/Update Version PR
-        id: changesets
         uses: changesets/action@v1
         with:
           title: 'chore(release): version packages'
@@ -58,10 +57,3 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ steps.app-token.outputs.token }}
           # npm authentication handled via OIDC trusted publishing (no token needed)
-
-      # Auto-merge the version PR when CI passes (reduces release to effectively 1 PR)
-      - name: Enable auto-merge for Version PR
-        if: steps.changesets.outputs.pullRequestNumber
-        run: gh pr merge ${{ steps.changesets.outputs.pullRequestNumber }} --auto --squash
-        env:
-          GH_TOKEN: ${{ steps.app-token.outputs.token }}